To begin with, the great tribulation begins when Michael, who is currently holding Satan, the son of perdition, at bay (2 Thess. 7), rises and casts that son of perdition, along with his angels, out of heaven and into this world (Rev. 12:7-9). Then there will be a period of spiritual affliction, extreme hardship, unlike anything that has ever occurred in the history of the nation:
"At that time Michael shall stand up, The great prince who stands watch over the sons of your people; And there shall be a time of trouble, Such as never was since there was a nation, Even to that time. And at that time your people shall be delivered, Every one who is found written in the book. - Daniel 12:1 (NKJV)
In Matthew 24, Jesus Christ sat’s it nearly word for word:
"For then there will be great tribulation, such as has not been since the beginning of the world until this time, no, nor ever shall be. - Matthew 24:21 (NKJV)
It's critical that you understand that there are two tribulations. The first tribulation is the appearance of the false messiah (antichrist) to deceive the world:
And war broke out in heaven: Michael and his angels fought with the dragon; and the dragon and his angels fought, but they did not prevail, nor was a place found for them in heaven any longer. So the great dragon was cast out, that serpent of old, called the Devil and Satan, who deceives the whole world; he was cast to the earth, and his angels were cast out with him. Then I heard a loud voice saying in heaven, "Now salvation, and strength, and the kingdom of our God, and the power of His Christ have come, for the accuser of our brethren, who accused them before our God day and night, has been cast down. - Revelation 12:7-10 (NKJV)
This is when Satan is physically cast out and appears in his role as the antichrist.
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Now look here…. The scripture below describes the second tribulation (Note: It says after that tribulation).
"But in those days, after that tribulation, the sun will be darkened, and the moon will not give its light; "the stars of heaven will fall, and the powers in the heavens will be shaken. "Then they will see the Son of Man coming in the clouds with great power and glory. "And then He will send His angels, and gather together His elect from the four winds, from the farthest part of earth to the farthest part of heaven. - Mark 13:24-27 (NKJV)
The four winds are associated with the time of the end, which is the second tribulation, God`s wrath, and this is when the battle of Armageddon and Hamon-gog take place.
Those battles will not last 15 minutes, because we don`t fight them; they are fought for us by God.
So there you have it, the two tribulations.