In fact there are multiple times of severe persecution and stress during the Christian Age.

“This know also, that in the last days perilous times shall come.”
2Tim 3:1 KJV.

The word “tribulation” means to be suffering, or under severe pressure. The Greek word is “thlip´-sis,” and it is a word used for being under pressure, much as we speak today. Some translations use the words “affliction” or “oppression.” Paul even says of all Christians,

“…that we must through much tribulation enter into the kingdom of God.”
Acts 14:22 KJV

So some stress is involved in being a true Christian. Further Jesus says,

“For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.” Mtt 24:21 KJV

Jesus associates this period of stress with the end of this present universe. 

“Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken:”
Mtt 24:29 KJV.

Jesus says “then” He will come.

“30 And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory. 31 And he shall send his angels with a great sound of a trumpet, and they shall gather together his electfrom the four winds, from one end of heaven to the other.”
Mtt 24:30-31 KJV

Yes there are two grand subjects in Matthew chapter 24: the destruction of Jerusalem in 70 AD, and the Second Coming of Christ. The “problem” (I speak as a man) is how to separate the two subjects. But notice that Mtt 24:30-31 is clearly about a time when “ all the tribes of the earth mourn, and … see” Jesus. And it is the time when Jesus shall gather his “elect” (the saved) “from one end of heaven to the other.” This also is something which clearly has not happened.

Also Rev 7:14 speaks of the “great tribulation.” The Greek here is very emphatic. If you translated it word for word it would be, “the great, the tribulation.”

Some want to maintain that the destruction of Jerusalem in 70 AD was the “great tribulation” of Mtt 24:21 which was worse than anything that will ever happen. But that of course makes nonsense of the Second Coming of Christ as clearly described in Mtt 24:30-31 which talks about “Immediately after the tribulation of those days.” As bad as 70 AD was, multiple events in history were worse than the destruction of Jerusalem in 70 AD. Prophecy Principles discusses this in more detail.

At best, the destruction of Jerusalem in 70 AD is a “type,” symbolic, a prototype, of the end of the world. The end of the world will in some respects “like” the destruction of Jerusalem in 70 AD. A “great” tribulation will precede the Second Coming of Christ.

This Great Tribulation is not some invention of men. This is Scripture.

KJV is the King James Version of 1611