The New Testament warned about the last days of man when it said the following.
1. Know this also, that in the last days perilous times shall come (2Timothy 3:1, HBFV throughout)
What is referenced as the Great Tribulation is actually composed of at least three main pieces. The first is the wrath and rule of Satan upon the earth that runs 3 1/2 years until the return of Christ. The second piece is composed of heavenly signs that begin when the sixth seal is open (Revelation 6:12 - 14). This relatively short period, possibly beginning 1 1/2 years after the devil's rule begins, heralds that a third major piece of the End Time will soon begin. This third section, referred to in the Bible as the Day of the Lord (Joel 2:11, 31, Malachi 4:5, 1Thessalonians 5:2, 2Peter 3:10, etc.), is the time when God directly punishes those on the earth who refuse to repent.
Why does God allow his chief adversary to rule the earth virtually unchecked, and be worshipped as if he were deity (Revelation 13:12, 15, 14:9, 11), for forty-two months? The primary reason this time of man's greatest affliction (Matthew 24:21) is allowed is as an eternal testimony, to both humans and angels, that Satan's way of life does NOT work!
of the End Time
War in Heaven
Satan and his demons are permanently cast out of heaven by God (through his holy angels). They will never be able to return (Revelation 12:7 - 9). The devil will no longer have access to the Almighty’s throne and be able to accuse those who are true Christians (verse 10). This casting down brings the full force of Satan's wrath upon the earth and begins what many refer to as the Great Tribulation.
Representatives of Satan and God
The Beast and the False Prophet begin their work of deceiving man and ruling the earth under the direct inspiration of the Devil (Revelation 13:3 - 15). God's Two Witnesses also begin their ministry of confronting these powerful individuals and calling upon all those on the earth to repent of their sins (Revelation 11:3 - 6).
A Place of Protection
Some (but by no means all) Christians are taken to a "place of safety" or protection for 3 1/2 years (Revelation 12:6, 14, 13:5). This location, somewhere on the earth (not in heaven), is where God shields some of his people from the horrors of Satan's world-ruling government. Those protected will be kept alive until they are changed to immortal spirit beings AFTER the return of Christ and the resurrection of all the dead saints throughout history (1Thessalonians 4:16 - 17, 1Corinthians 15:51 - 53).
Mark of the Beast
Soon after the Beast and False Prophet take control over the world, they demand all humans receive a "mark." This mark symbolizes a person's willingness to worship the Beast and obey the new one world system. Those who refuse to accept this mark will not only be unable to buy or sell anything, they will be hunted down for their disobedience and killed (Revelation 13:14 - 17).
Martyrdom of Saints
In spite of what many religious organizations teach, not all Christians are whisked away in some secret rapture to be protected from the devil's wrath. The Bible clearly states that not only will true believers exist on the earth during the Tribulation period, many of them (most? all?) will reject the Beast's mark. This will make them targets for persecution, which will ultimately lead to them receiving the death penalty for their disobedience against the one world state (Matthew 24:9, Revelation 6:11, 12:11, 17, 13:7, 14:12 - 13).
Signs in the heavens appear as a warning that God's wrath upon unrepentant sinners will soon arrive. The sun will be darkened, the moon will no longer reflect light, stars will seem like they are falling to earth and other calamities will occur (Matthew 24:29, Joel 2:30 - 31, Revelation 6:12 - 14).
Sealing of 144,000 and the Innumerable Multitude
Just before the beginning of the prophetic "Day of the Lord" 144,000 people, or twelve thousand each from twelve of Israel's thirteen tribes (the tribe of Dan excluded) are converted or "sealed" (Revelation 7:1 - 8). In addition, a "great multitude" of other people are also brought to repentance and become obedient to the Eternal (verses 9 - 17).
The Day of the Lord
This period of time represents God's personal intervention and judgment against those who refuse to repent. God's wrath against sin begins with seven trumpet blasts the each herald a particular penalty brought on the earth (Revelation 8 - 9) and ends with seven final plagues (Revelation 16, 18).
Death of the Two Witnesses
During their 3 1/2 year ministry the Two Witnesses are protected from all harm by God. During their ministry they are given the unique ability to instantly kill anyone who opposes them, to stop rain from falling on the earth and given other supernatural powers (Revelation 11:3 - 6). Their ministry ends when God removes his protection from them and allows the Beast power to kill them in Jerusalem (verses 7 - 9). Although the earth rejoices at their deaths, they are soon brought miraculously back to life. After their resurrection, they ascend to meet Jesus in the clouds (verses 10 - 12).
The First Resurrection
The Two Witnesses are (highly likely) the first people brought back to life in what Scripture calls the first resurrection. The "dead in Christ," all those who from Adam obeyed God and are deemed worthy, are the next to be resurrected. Finally, those who have been alive and protected by God in a "place of safety" are instantaneously changed from flesh to immortal spirit (Revelation 11:10 - 12, 1Thessalonians 4:16 - 17, 1Corinthians 15:51 - 53).
Jesus returns and Babylon falls!
Satan's version of God's kingdom, which has lasted for 3 1/2 years, is brought to a complete end. Jesus returns to the earth a second time, with an army of resurrected humans who are now composed of spirit, to fight and overcome the Beast and the False Prophet (Revelation 19:14 - 21). This climatic battle will take place in the valley of Megiddo (from which we get the word Armageddon, Revelation 16:12 - 16).
A Fiery End
The army of the Lord takes control of the earth. The Beast and the False Prophet are caught and thrown alive into a lake of fire (Revelation 19:20)
Silence of the Deceiver
Satan the devil, the author of sin who deceived countless others into disobeying God, is caught and placed in a spiritual prison for 1,000 years (Revelation 20:1 - 2). In this place of imprisonment he will not be able to deceive anyone (except, of course, himself).
Jesus begins to reign as King of Kings and Lord of Lords (Revelation 19:16) over the earth. He will establish God's Kingdom on the planet and bring an unparalleled 1,000 years (the word Millennium means 1,000 years) of peace and prosperity to all humans.