Studying the Book of Revelation carries with it a promise:
Blessed is he who reads and those who hear the words of this prophecy, and keep those things which are written in it; for the time is near (Revelation 1:3)

The Book is basically written in chronological order (See 8:13, 9:12; 10:7, 11:14):
I heard an angel flying through the midst of heaven, saying with a loud voice, Woe, woe, woe to the inhabitants of the earth, because of the remaining blasts of the trumpet of the three angels who are about to sound! (8:13).
The 3 Woes are the last 3 Trumpets.
The first woe (5th Trumpet) is past. Two other woes (6th and 7th Trumpet) are yet to come (9:12).
The second woe (6th Trumpet) is past. Behold, the third woe (7th Trumpet) is coming quickly (11:14).
During the time of the 6th Trumpet a mighty angel announces: There will be no more delay.  In the days of the sounding of the 7th angel, who is about to sound (the 7th Trumpet), the mystery (the sealed Tribulation judgements) of God would be finished (10:6,7).

1:19 gives the basic outline:
(1) The things which you have seen (the past vision of Christ in chapter 1)
(2) the things which are (now) (the Church-Age in chapters 2 and 3)
(3) the things which shall be after this (after the Church Age).

Revelation 4:1 refers to a rapture where John is told he will now see the things which must be after this.
Thus Revelation 4-21, describe events after the Church-Age.
In Revelation 4 and 5 we see the Church in Heaven and the Seals about to be opened, which start the Tribulation in chapter 6.
Revelation 6-19 then describes the Tribulation.

The intensity of these times will be unprecedented.  With so many things happening at once, as everything comes to a climax, it is clearly very difficult to give a clear orderly account.   Therefore, the writer of the Book of Revelation uses three techniques, and the result is a masterpiece.

The three techniques:
(1) Series of SEVENS are used to give the chronological framework and to move the story forward:
7 CHURCHES - 7 SEALS- 7 TRUMPETS - 7 BOWLS
Events are dated according to which Seal, Trumpet and Bowl they occur in.

(2) HEAVENLY INTERLUDES take place before each major transition to a new phase, which emphasise Divine Sovereignty and control, demonstrating that we see that what happens on earth is controlled from Heaven.  This helps us to keep a heavenly perspective.  It is war and God is the General running His Battle Campaign from Heaven, with men and angels playing their part.   As well as the main interludes, every time we see a Seal  opened, a Trumpet blown or a Bowl poured out, we are in a heavenly interlude.  Generally during a heavenly interlude, effectively no time passes on earth. 

Revelation 4 and 5 in particular reveal Heaven as the Control Centre.  
John receives a vision of heaven just after the close of the Church-Age (Rev 2&3), and therefore just at the start of the Tribulation.   The events on earth are subject to the events in heaven.

Revelation 4:1-11 describe the Throne of God:
After these things I looked, and behold, a door standing open in Heaven.
And the first voice which I heard was like a trumpet speaking with me, saying,
Come up here, and I will show you things which must take place after this.  Immediately I was in the Spirit;
This catching-up of John is a picture of the Rapture of the Church to Heaven.

The Throne of God-the Control Centre of the Universe
And behold, a Throne set in Heaven, and One sat on the Throne.
And He who sat there was (1) like a JASPER (transparent diamond = purity)
and (2) a SARDIUS stone (red) in appearance;
and (3) there was a RAINBOW around the Throne, in appearance like an EMERALD (green).
With all the glory, energy and light shining around the Throne he found it hard to describe.  The best way he could describe God was as precious sparkling stones, shining with God’s glory.  He sees the Trinity: 3 glorious lights: two were on the Throne (the Father and Son), and the third radiated out from the Throne (the Holy-Spirit), surrounding the Throne as an emerald Rainbow.   This is a wonderful representation of the Triune God who is One in Three and Three in One.  
The pure white (holy) DIAMOND shining with the glory of God represents GOD, the FATHER.  
The blood red sparkling SARDIUS stone represents GOD, the SON, the sacrificial Lamb slain.
The green EMERALD RAINBOW, is GOD, the HOLY-SPIRIT, Who is not on the Throne but is centred on it and radiates out from it. This Rainbow forms a complete circle, signifying God’s eternal covenant of love and grace towards man, based on the propitiation of Christ (natural rainbows are also full circles when seen from high up- from God’s viewpoint). Green is the colour of grace and life. The many colours show the multi-faceted, lifegiving covenant grace of God  (healing, victory, joy, love, wisdom, peace..) given to us - radiating out from the Father, through the Son, in the Holy-Spirit.  So we see the Throne in Heaven is a Throne of Grace for believers, through the propitiation of Christ.   The Rainbow’s 7 primary colours are the perfection of holiness (God’s character) given to us in the Covenant, as revealed in the 7 Covenant (‘I Am’) Names of the Lord. Thus the Spirit radiates out from the Father and Son as the Spirit of Grace.  God’s glory originates in the pure white love and holiness of the Father (the Diamond), but if it came to us direct, it would destroy us.  So, it comes through the
Son, filtered through the red blood of the Lamb (propitiation), radiating out to us from the Throne in the Holy-Spirit in the many different colours of grace.  This is the true Rainbow of which Noah’s was just a shadow. The rainbow of Noah's covenant is a type of this Rainbow.  A similar image of the Throne and the Triune God is in Rev 22:1 where we see the Throne of God the Father and the Lamb (the Son), from which the Holy-Spirit (the River of Life) flows.

The 24 Elders represent the Church, therefore the Church is now raptured to Heaven.
Around the throne were 24 thrones, and on the thrones I saw 24 elders sitting,
clothed in white robes; and they had crowns of gold on their heads.

The Throne is also a Throne of judgement upon evildoers, especially in the Tribulation.
And from the Throne proceeded lightnings, thunderings, and voices.
7 lamps of fire were burning before the Throne, which are the 7-fold Spirit of God (described in 5:6, as 7 eyes which see everything ).  Before the Throne there was a sea of glass, like crystal.

Heaven is a place of continual worship to God
And in the midst of the Throne, and around the Throne, were four living creatures full of eyes in front and in back.
The first living creature was like a lion, the second living creature like a calf,
the third living creature had a face like a man, and the fourth living creature was like a flying eagle.
The four living creatures, each having six wings, were full of eyes around and within.
And they do not rest day or night, saying: Holy, holy, holy, Lord God Almighty, Who was and is and is to come!
Whenever the living creatures give glory and honour and thanks to Him who sits on the Throne,
who lives forever and ever, the 24 fall down before Him who sits on the Throne
and worship Him who lives forever and ever, and cast their crowns before the Throne, saying: 
You are worthy, O Lord, to receive glory and honour and power;
For You created all things, and by Your will they exist and were created .
It is just after the Rapture and we see Heaven initiating the start of the Tribulation on earth (see Revelation 6). 

In Revelation 5:1, God holds a Scroll with Seven Seals. It is the Title-Deed of the earth, containing God’s Plan to judge evil and establish His Kingdom: And I saw in the right hand of Him who sat on the Throne, a Scroll written inside and on the back, sealed with 7 Seals.  Whoever has this Scroll has the right to bring God’s Plan to pass, but who is worthy to open its Seals?    Then I saw a strong angel proclaiming with a loud voice, Who is worthy to open the Scroll and to loose its Seals?  And no one in heaven or on the earth or under the earth was able to open the Scroll, or to look at it.
So I wept much, because no one was found worthy to open and read the Scroll, or to look at it (5:2-4).

Only One was found to be worthy- Jesus Christ, the Lamb of God: But one of the elders said to me, Do not weep.
Behold, the Lion of the tribe of Judah, the Root of David, has prevailed to open the Scroll and to loose its 7 Seals.
And I looked, and behold, in the midst of the Throne and of the 4 living creatures, and in the midst of the elders, stood a Lamb as though it had been slain (signifying He is now a resurrected Lamb), having 7 horns (possessing all authority in heaven and earth) and 7 eyes, which are the 7 Spirits of God (or the 7-fold Spirit of God) sent out into all the earth (signifying perfect knowledge and wisdom through the fullness of the Spirit) - v5,6.   Jesus Christ alone is worthy to judge the world, take dominion of the earth and reign as King of kings.  His worthiness is not just because He is the eternal God, but because He also became a man, and as a man prevailed against all opposition, overcoming sin, satan and death for us.  He came to die for our sins and to redeem us to God.  Thus, being now the glorified God-man, He is fully qualified to judge men with perfect knowledge, justice and mercy.  He is now worthy to rule as a LION, because He suffered for us as a sacrificial LAMB.  The songs of praise in v8-14 confirm this.

He took the Scroll signifying that He will now execute God’s plans and judgements:
Then He came and took the Scroll out of the right hand of Him who sat on the Throne (v7).    

This results in great praise in Heaven: Now when He had taken the Scroll, the 4 living creatures and the 24 elders fell down before the Lamb, each having a harp, and golden bowls full of incense, which are the prayers of the saints. And they sang a new song, saying: You are worthy to take the scroll, and to open its seals; for You were slain, and have redeemed us to God by Your blood Out of every tribe and tongue and people and nation, and have made us kings and priests to our God; and we shall reign on the earth. Then I looked, and I heard the voice of many angels around the throne, the living creatures, and the elders; and the number of them was ten thousand times ten thousand, and thousands of thousands, saying with a loud voice: Worthy is the Lamb who was slain to receive power and riches and wisdom, and strength and honour and glory and blessing!   And every creature which is in heaven and on the earth and under the earth and such as are in the sea, and all that are in them, I heard saying: Blessing and honour and glory and power be to Him who sits on the throne, and to the Lamb, forever and ever!  Then the 4 living creatures said, Amen! And the 24 elders fell down and worshipped Him who lives forever and ever (v8-14).  

As He begins to open the Seals in Heaven, the Tribulation begins on earth: Now I saw when the Lamb opened one of the seals; and I heard one of the four living creatures saying with a voice like thunder, Come and see (6:1).
As more of the Scroll is opened and read, the corresponding events take place on earth, until at the end all sin is removed and God’s Kingdom is fully established on earth.  Thus the reading of the Scroll in Heaven controls the action on earth, as God moves to remove His enemies and reestablish His Kingdom here.  Therefore the contents of the Scroll are described in Revelation 6-22, for the final events that unfold on the earth reveal what is written.

This gives us insight into the nature of the Tribulation.  The earth belongs to God but has fallen into evil hands.  The time has come for Him to repossess His house, to retake what is His, to reestablish His dominion on earth through His Christ.  For this to happen there must be open warfare against the entrenched forces in the world that resist God.   This time of warfare is the Tribulation.  Wars are fought to gain dominion and territory. The real war taking place in the Tribulation is between God’s Kingdom and satan’s kingdom and the battle is for dominion of the earth.   For the new level of dominion in the Millennium to be established, Christ must take on and overcome all resistance.   In the Tribulation God is advancing against the powers of darkness controlling this world.  Meanwhile satan is doing all he can to strengthen his hold and dominion on the world.   It will be a time of great trouble.  The sufferings of the Tribulation are called 'birth-pains', for it is like a new baby (the Kingdom) coming through from the unseen (spiritual) realm into open manifestation.   The result of this baby pushing through against much resistance, is that great pains and shaking are set up in the earth that increase in intensity until the baby is born.

The confrontation of God with the kingdom of Egypt provides a type of the Tribulation.  God’s people were being oppressed and persecuted.  God sent Moses (a picture of Jesus) who initiated the judgments of God on the evil kingdom.  The 10 plagues exposed and broke the power of the ‘gods’ of Egypt (satan and his demons).   Pharaoh (antichrist) increased his persecution of God’s people, ultimately trying to annihilate them.   But in the act of doing this (as at Armageddon) he and his armies are destroyed by God’s intervention.   With Egypt’s dominion broken, Israel are delivered, enter a new covenant with God and possess the Promised Land (the Millennial Kingdom).   The Tribulation judgments are foreshadowed by the 10 plagues only they are on a world-wide scale rather than just a national scale.

(3) THE MAIN CHARACTERS are introduced at appropriate moments as the story unfolds.  They are usually introduced when events centre on them.  At these points the writer takes a 'time-out' to tell us more about the relevant character, giving their background his activities leading up to that time in a flash-back, before describing what they will do and acheive from that time on.   The end result is a work of genius!  The framework of Seals, Trumpets and Bowls show God’s overall control in driving things forward to their climax.  It is a chronological account (events are described in their order), with the central story controlled by God’s Seal, Trumpet and Bowl judgements.  But rather than giving a strict order of events, greater insight and interest are achieved by inserting interludes showing the heavenly activities that control events, as well as other interludes revealing the earthly activities of the main characters when they are introduced into the story.   Recognising these interludes (parentheses), is essential to understanding the flow of the Book.

THE SEALS, TRUMPETS and BOWLS
The opening of the Seals in Heaven initiates the Tribulation on earth.  
The 7 Seals contain everything. 
The 7th Seal contains the 7 Trumpets. 
The 7th Trumpet contains the 7 Bowls.  
Therefore each transition represents an escalation of the War.   After the 6th Seal and the 6th Trumpet there is a special heavenly interlude, indicating that God is moving things onto the next level.

SEAL 1
SEAL 2
SEAL 3
SEAL 4
SEAL 5
SEAL 6
SEAL 7 -- TRUMPET  1
                T RUMPET  2
                T RUMPET  3
                T RUMPET  4
                T RUMPET  5
                T RUMPET  6
                T RUMPET  7---- BOWL 1
                                           BOWL 2
                                           BOWL 3
                                           BOWL 4
                                           BOWL 5
                                           BOWL 6
                                           BOWL 7
 

THE CHRONOLOGY OF THE TRIBULATION (Revelation 6-19).
Each stage represents an escalation of trouble.  The Seals reveal the results of God's judgements that will continue through the whole of the Tribulation increasing in intensity (as birth-pains).  The loosing of the first six Seals reveal the various results of the removal of God’s restraint on evil.  The first 6 Seals are opened quickly at the start of the Tribulation.   We have already noted in Part 1 that these Seals exactly match Matthew 24:7-10 and Luke 21:11 which describe 'the beginning of the sorrows (birth-pains)’ of the Tribulation. In other words these are the predicted events for the first half of the Tribulation ('the beginning of sorrows'), which will also continue and increase to their climax in the second-half (the Great-Tribulation).  The 7th Seal introduces the 7 Trumpet judgements, which are direct judgements from God announced by the 2 witnesses.  

Revelation 6: The SEALS
The first four Seals = the four Horsemen

*SEAL 1, releases the antichrist to rise to world-power (Matthew 24:7):
I saw when the Lamb opened one of the Seals, and I heard, as it were the noise of thunder, one of the four beasts saying, Come and see.   And I saw, and behold a white horse: and he that sat on him had a bow; and a crown was given unto him: and he went forth conquering, and to conquer (Revelation 6:1-2).
This describes antichrist setting out to gain world-conquest, right at the start of the Tribulation.

*SEAL 2.   The result is World War and great bloodshed (Matthew 24:7):
When He (Christ) had opened the 2nd Seal, I heard the second beast say, Come and see. And there went out another horse that was red: and power was given to him that sat thereon to take peace from the earth, and that they should kill one another: and there was given unto him a great sword (Revelation 6:3-4).

 *SEAL 3.  The result of this War is great famine (Matthew 24:7): When He (Christ) had opened the 3rd Seal, I heard the third beast say, Come and see. And I beheld, and lo a black horse; and he that sat on him had a pair of balances in his hand. And I heard a voice in the midst of the four beasts say, A measure of wheat for a penny, and three measures of barley for a penny; and see thou hurt not the oil and the wine (Revelation 6:5-6).

*SEAL 4.  The result of all this is the death of a quarter of the earth’s population (Matthew 24:7):
When He (Christ) had opened the 4th Seal, I heard the voice of the 4th beast say, Come and see’. And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him.   And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth (Revelation 6:7-8).

*SEAL 5 reveals increasing persecutions and martyrdoms of believers even from early in the Tribulation (Matt 24:9,10):
When He (Christ) had opened the 5th Seal, I saw under the altar the souls of them who were slain for the word of God, and for the testimony (to Christ) which they held: and they cried with a loud voice, saying, How long, O Lord, holy and true, do You not judge and avenge our blood on those who dwell on the earth? And white robes were given unto every one of them; and it was said unto them, that they should rest yet for a little season, until their fellowservants also and their brethren, that should be killed as they were, should be completed (Rev 6:9-11).
These are the martyrs from the first half of the Tribulation.   Many of them are the victims of Mystery Babylon, the apostate, harlot church that gains great power from the beast-kingdom in the first-half of the Tribulation (Rev 17:6), before being destroyed by it at Mid-Tribulation, when the new universal religion of worshipping the antichrist is introduced (17:16,17). There will be even more martyrdoms in the Great-Tribulation, which are committed by the antichrist-system.  They are under the altar because they have poured their lives out as a sacrifice to God.  They pray for the Lord to return to avenge them, but they are told they must first wait until the full number of martyrs are killed.  They must wait for the martyrs from the Great Tribulation to join them (Revelation 7:9-17) - a far greater number of believers.  The blood of all these martyrs is a major cause of God’s judgements falling upon the earth in the Tribulation with greater and greater intensity, until the Lord Himself takes final vengeance on the evildoers in His Second Coming (16:4-7).   They are souls without bodies, but God gives them white robes until they receive their resurrection bodies.   These verses show there is an Intermediate State between death and resurrection, where men are conscious.  For believers it is a time of rest and worship.

*SEAL 6 reveals the wrath of God, causing great and unusual convulsions of nature (Matt24:7, Luke21:11) that grow in intensity through the Tribulation, until the scene described in Revelation 6:12-17, which happens just before the Second Coming of Christ:  I looked when He opened the 6th Seal, and behold, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became like blood.  And the stars of heaven fell to the earth, as a fig tree drops its late figs when it is shaken by a mighty wind.  Then the sky receded as a scroll when it is rolled up, and every mountain and island was moved out of its place. And the kings of the earth, the great men, the rich men, the commanders, the mighty men, every slave and every free man, hid themselves in the caves and in the rocks of the mountains, and said to the mountains and rocks, Fall on us and hide us from the face of Him who sits on the Throne and from the wrath of the Lamb!  For the Great Day of His Wrath has come, and who is able to stand?

Revelation 7 - THE GOSPEL GOES FORTH.  
Before the 7th Seal there is an Interlude revealing God’s programme of  World-Wide Evangelism for the Tribulation.

Firstly, the 144,000 JEWISH EVANGELISTS are introduced who spearhead this outreach (7:1-8).  
In the 6th Seal, early in the Tribulation, we see them anointed and sealed (given Divine protection so that they can fulfil their ministry). They are sealed before the 7th Seal because this Seal contains the Trumpet Judgements and the evangelists need to be sealed (protected) from the coming Trumpet Judgments before they begin:  
After these things I saw 4 angels standing on the 4 corners of the earth, holding the 4 winds of the earth, that the wind should not blow on the earth, nor on the sea, nor on any tree (the targets of the first 4 Trumpets. Thus they are protected from the first 4 Trumpets.  They are also protected from the 5th and 6th Trumpets - see Revelation 9:1-4). 
And I saw another angel ascending from the east, having the seal of the living God:
and he cried with a loud voice to the four angels, to whom it was given to hurt the earth and the sea (these are the first 4 Trumpet angels who will sound in quick succession), saying, Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads.  And I heard the number of them which were sealed:
and there were sealed 144,000 of all the tribes of the children of Israel (v1-4).  

There are 12,000 from each tribe, emphasising that they are of Israel:
of the tribe of Judah 12,000 were sealed;
of the tribe of Reuben 12000 were sealed;
of the tribe of Gad 12000 were sealed;
of the tribe of Asher 12000 were sealed;
of the tribe of Naphtali 12000 were sealed;
of the tribe of Manasseh 12000 were sealed;
of the tribe of Simeon 12000 were sealed;
of the tribe of Levi 12000 were sealed;
of the tribe of Issachar 12000 were sealed;
of the tribe of Zebulun 12000 were sealed;
of the tribe of Joseph 12000 were sealed;
of the tribe of Benjamin 12000 were sealed (v5-8).
This clearly identifies them as being of Israel.  These evangelists will be like the apostle Paul.   They will already have a good knowledge of the Scriptures (many will be orthodox Jews).    After the Rapture, they will have a sudden realisation that Jesus is the Christ.  They will have a supernatural encounter with God and be anointed for a powerful ministry.  They will all be celibate, so that they can be fully devoted to their mission (see Revelation 14:1-5).  They will spearhead God’s evangelistic programme in the first half of the Tribulation.  This shows that the Church is not present, for evangelism is again entrusted to Israel (the Tribulation is the final seven years of the 490 years allotted to Israel - Daniel 9:24).

THE  TRIBULATION MARTYRS.  Then, we see a great number of their converts in Heaven, who are mostly martyred in the Great Tribulation, because they refused to follow and worship the Beast.  The evangelists and their converts fulfill Matthew 24:14 in the first half of the Tribulation.  We saw that the early Tribulation martyrs were told to wait until their number was complete (Revelation 6:9-11).  Now a much greater number of martyrs (the fruit of the ministry of the 144,000) is seen in Heaven in Revelation 7:9-17, redeemed from every nation: After these things I looked, and behold, a great multitude which no one could number, of all nations, tribes, peoples, and tongues, standing before the Throne and before the Lamb, clothed with white robes (just like the martyrs of 6:9-11), with palm branches in their hands, and crying out with a loud voice, saying, Salvation belongs to our God who sits on the Throne, and to the Lamb! 
All the angels stood around the Throne and the elders and the four living creatures, and fell on their faces before the Throne and worshipped God, saying: Amen! Blessing and glory and wisdom, thanksgiving and honour and power and might, be to our God forever and ever. Amen.   Then one of the elders answered, saying to me,
Who are these arrayed in white robes, and where did they come from?  And I said to him, Sir, you know. 
So he said to me, These are the ones who come out (literally: are coming out) of the Great Tribulation, and washed their robes and made them white in the blood of the Lamb.  Therefore they are before the Throne of God, and serve Him day and night in His Temple.   And He who sits on the Throne will dwell among them.  They shall neither hunger anymore nor thirst anymore; the sun shall not strike them, nor any heat;  for the Lamb who is in the midst of the Throne will shepherd them and lead them to living fountains of waters.   God will wipe away every tear from their eyes.  We will later see these will be resurrected and rewarded at the Return of Christ (Rev 20:4).  These visions of the martyrs show their importance to God and prove that the doctrine of soul-sleep is false. They are conscious and active, and although they do not yet have a body they are given white robes to wear, to cover their souls.

Revelation 8
*SEAL 7:  And when He (Christ) had opened the 7th Seal, there was silence in heaven about the space of half an hour (Rev 8:1).   This fearful silence indicates an escalation of judgement is about to begin.  This 7th Seal reveals the 7 Trumpets which release abnormal disturbances of nature, missiles from Heaven (including massive meteorites) and demonic invasions from the Abyss:  And I saw the 7 angels who stand before God, and to them were given 7 Trumpets.
Then another Angel, having a golden censer, came and stood at the altar. He was given much incense,
that he should offer it with the prayers of all the saints upon the golden altar which was before the throne.  
And the smoke of the incense, with the prayers of the saints, ascended before God from the Angel's hand.  
Then the Angel took the censer, filled it with fire from the altar, and threw it to the earth. And there were noises, thunderings, lightnings, and an earthquake.  So the 7 angels who had the 7 trumpets prepared themselves to sound (8:2-6).  The Trumpets are direct special successive judgements from heaven, that only last for a certain time before the next one begins (unlike the Seals which describe conditions throughout the Tribulation).  Thus they come one after the other throughout the first-half of the Tribulation (8:13; 9:5,12,15; 10:7; 11:14).   The 7th Trumpet will open the Great-Tribulation and its days continue until its end, for all the remaining judgements, including the Bowls, are contained within it (10:7)..
 
THE TRUMPETS 
*TRUMPET 1 (8:7)  A third of vegetation is destroyed by hail:  The first angel sounded, and there followed hail and fire mingled with blood, and they were cast upon the earth: and the third part of trees was burnt up, and all green grass was burnt up.

*TRUMPET 2 (8:8,9) A third of sea life destroyed (by a meteorite): The 2nd angel sounded, and as it were a great mountain burning with fire was cast into the sea: and the third part of the sea became blood; and the third part of the creatures which were in the sea, and had life, died; and the third part of the ships were destroyed.

*TRUMPET 3 (8:10,11) A third of fresh-water made bitter:
The 3rd angel sounded, and there fell a great star from heaven, burning as it were a lamp, and it fell upon the 3rd part of the rivers, and upon the fountains of waters; and the name of the star is called Wormwood (the name of a bitter, poisonous herb, symbolising the results of sin - Jer9:15, 23:15): and the third part of the waters became wormwood; and many men died of the waters, because they were made bitter.

*TRUMPET 4 (8:12) A third of light lost: The 4th angel sounded, and the third part of the sun was smitten, and the third part of the moon, and the third part of the stars; so as the third part of them was darkened, and the day shone not for a third part of it, and the night likewise.

Revelation 8:13 marks another escalation of judgement. The last 3 Trumpets are introduced as the 3 Woes:
I beheld, and heard an angel flying through the midst of heaven, saying with a loud voice, Woe, woe, woe, to the inhabiters of the earth by reason of the other voices of the Trumpet of the three angels, which are yet to sound!

Revelation 9
*TRUMPET  5 = WOE 1 (9:1-12):   Then the 5th angel sounded:
And I saw a star fallen from heaven to the earth. To him was given the key to the bottomless pit.
And he opened the bottomless pit, and smoke arose out of the pit like the smoke of a great furnace. So the sun and the air were darkened because of the smoke of the pit.  Then out of the smoke locusts came upon the earth. And to them was given power, as the scorpions of the earth have power.  They were commanded not to harm the grass of the earth, or any green thing, or any tree, but only those men who do not have the seal of God on their foreheads.  And they were not given authority to kill them, but to torment them for 5 months. Their torment was like the torment of a scorpion when it strikes a man.  In those days men will seek death and will not find it; they will desire to die, and death will flee from them.  The shape of the locusts was like horses prepared for battle. On their heads were crowns of something like gold, and their faces were like the faces of men.  They had hair like women's hair, and their teeth were like lions' teeth. And they had breastplates like breastplates of iron, and the sound of their wings was like the sound of chariots with many horses running into battle.  They had tails like scorpions, and there were stings in their tails. Their power was to hurt men five months. And they had as king over them the angel of the bottomless pit, whose name in Hebrew is Abaddon, but in Greek he has the name Apollyon.
One woe is past. Behold, still 2 more woes are coming after these things.  This is a demonic invasion from the Abyss, resulting in men being tormented for 5 months.  The fact that the world blamed the 2 Witnesses for these torments (11:10) shows that as God's prophets they announce the Trumpet judgements in advance.

*TRUMPET 6 = WOE 2  (9:13-21):  Then the sixth angel sounded:
And I heard a voice from the four horns of the golden altar which is before God, saying to the sixth angel who had the trumpet, Release the four angels who are bound at the great river Euphrates.  So the four angels, who had been prepared for the hour and day and month and year, were released to kill a third of mankind.  Now the number of the army of the horsemen was two hundred million; I heard the number of them.  And thus I saw the horses in the vision: those who sat on them had breastplates of fiery red, hyacinth blue, and sulfur yellow; and the heads of the horses were like the heads of lions; and out of their mouths came fire, smoke, and brimstone.  By these three plagues a third of mankind was killed-by the fire and the smoke and the brimstone which came out of their mouths. For their power is in their mouth and in their tails; for their tails are like serpents, having heads; and with them they do harm. But the rest of mankind, who were not killed by these plagues, did not repent of the works of their hands, that they should not worship demons, and idols of gold, silver, brass, stone, and wood, which can neither see nor hear nor walk. And they did not repent of their murders or their sorceries or their sexual immorality or their thefts.  This is another demonic invasion, but much worse than the previous one, resulting in a third of mankind being killed.  Combine this with the death count from the 4th Seal (a quarter of mankind is killed from wars, famines and disease during the Tribulation), and the many martyrdoms, and we can see that the Tribulation will be marked by disasters on a scale far greater than anything else the world has ever seen!  We can deduce that almost half of the world’s population is killed in the first half of the Tribulation alone, and the second half is even worse in its horror!  

MID_TRIBULATION - Revelation 10