The tribulation is a seven year period spoken of by the prophet Daniel around the year 600 BC.
In Daniel 9:24-27, Daniel says that someday a decree will be made to rebuild the walls of Jerusalem. Sixty-nine prophetic "weeks" after that decree, the Messiah would make His first coming. A prophetic week has always meant seven Hebrew years of 360 days per year. Then He would be "cut off." Thus, 69 "weeks equals 69 X 7 = 483 years X 360 days = 173,880 days.
The only major decree to rebuild the walls of Jerusalem recorded in history is the decree of Artaxerxes Longimanus (Neh. 2:1), on May 14, 445 BC. Add the day Yeshua [Jesus] made His triumphal entry into Jerusalem on a foal. Needless to say, Daniel's prediction over 600 years earlier was fulfilled to the exact day. Messiah was cut off--crucified, resurrected, and ascended from the Mount of Olives. As He ascended into heaven, He promised to descend on the same mountain when He returned to Earth for His Second Coming....at which time He would conquer planet Earth and make Jerusalem His world capital. (The Third Millennium, Dr. Paul Meier, p 302)[Any references here or further in this writing to Dr. Meier's fictional book on how the end times may affect a family is taken from his appendix in which he explains many of these non-fictional passages from the bible.]
(Dan 9:25) "Know therefore and understand, That from the going forth of the command To restore and build Jerusalem Until Messiah the Prince, There shall be seven weeks and sixty-two weeks; The street shall be built again, and the wall, Even in troublesome times.
Note that the previous prophecy is one of many to predict Jesus' first coming. However, it is also pointing to His second coming!
(Dan 9:26) "And after the sixty-two weeks (seven plus sixty-two weeks) Messiah shall be cut off, but not for Himself; And the people of the prince who is to come Shall destroy the city and the sanctuary. The end of it shall be with a flood, And till the end of the war desolations are determined. (paren. mine; emphasis mine)
The final, seventh, week is the one stated in verse 27. This seventieth week of Daniel will be made apparent by Antichrist, the leader of the Revived Roman Empire, confirming a seven year peace treaty with Israel.(See Topic, European Union, for more information on the rived Roman Empire)
(Dan 9:27) Then he shall confirm a covenant with many for one week; But in the middle of the week He shall bring an end to sacrifice and offering. And on the wing of abominations shall be one who makes desolate, Even until the consummation, which is determined, Is poured out on the desolate."
There are many other references to this last "week" or seven years in the book of Revelation. The first 3 1/2 years of this treaty are relatively peaceful years although the natural disasters we are experiencing now will be intensified. It is after this period when the Great Tribulation occurs of 3 1/2 years. This period is filled with many natural and man made disasters. Since the writing of this book, many bible scholars were forced into interpreting these passages symbolically. They could never fathom its true meaning because of ignorance of the incredible capabilities of modern technology. This technology will be used to its capacity by the coming Antichrist.
The end of the first 3 1/2 year period is marked by the breaking of the peace treaty by Antichrist. He does this by desecrating the newly re-built temple in Jerusalem and declaring himself a god in the holy of holies. See Daniel 9:27 above. This will not seem so unusual considering the widespread teaching of the New Age movement which proclaims all things to be divinity. Many New Age beliefs are being taught and accepted in our schools and our workplaces all over the world. From the time the temple is desecrated, one can count exactly 3/12 years, 1260 days, until the second coming of Christ! But what a horrifying 3 1/2 years it will be. It will be the most destructive the world has ever known and the target of Antichrist will be Christians and Jews alike.
(Rev 13:5-8) And he was given a mouth speaking great things and blasphemies, and he was given authority to continue for forty-two months. {6} Then he opened his mouth in blasphemy against God, to blaspheme His name, His tabernacle, and those who dwell in heaven. {7} It was granted to him to make war with the saints and to overcome them. And authority was given him over every tribe, tongue, and nation. {8} All who dwell on the earth will worship him, whose names have not been written in the Book of Life of the Lamb slain from the foundation of the world.