Some, like myself already see the tribulation (a.k.a., the day of the Lord) having commenced. There hasn't been this number of displaced people throughout the world since the end of WWII, and these numbers are growing daily. Economies are imploding, and starvation is increasing. Even here in the U.S., tens of millions are now without work, are short on food, and on the verge of being evicted. If this isn't tribulation for the billion or so people throughout the world experiencing some of these situations, then I'm not entirely sure what does constitute tribulation. It still isn't at the level where it is the worst of times that have ever been as the Bible tells us will be, but it definitely seems to be getting there fast.
There will be a future human man who will be revealed as the Jewish Messiah, when this (Man Of Sin) is revealed in Jerusalem, the 3.5 year tribulation starts, this is a cake walk, compared to what's coming for the wicked.
Revelation 9:2-6KJV
2 And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air were darkened by reason of the smoke of the pit.
3 And there came out of the smoke locusts upon the earth: and unto them was given power, as the scorpions of the earth have power.
4 And it was commanded them that they should not hurt the grass of the earth, neither any green thing, neither any tree; but only those men which have not the seal of God in their foreheads.
5 And to them it was given that they should not kill them, but that they should be tormented five months: and their torment was as the torment of a scorpion, when he striketh a man.
6 And in those days shall men seek death, and shall not find it; and shall desire to die, and death shall flee from them.
Revelation 16:1-9KJV
1 And I heard a great voice out of the temple saying to the seven angels, Go your ways, and pour out the vials of the wrath of God upon the earth.
2 And the first went, and poured out his vial upon the earth; and there fell a noisome and grievous sore upon the men which had the mark of the beast, and upon them which worshipped his image.
3 And the second angel poured out his vial upon the sea; and it became as the blood of a dead man: and every living soul died in the sea.
4 And the third angel poured out his vial upon the rivers and fountains of waters; and they became blood.
5 And I heard the angel of the waters say, Thou art righteous, O Lord, which art, and wast, and shalt be, because thou hast judged thus.
6 For they have shed the blood of saints and prophets, and thou hast given them blood to drink; for they are worthy.
7 And I heard another out of the altar say, Even so, Lord God Almighty, true and righteous are thy judgments.
8 And the fourth angel poured out his vial upon the sun; and power was given unto him to scorch men with fire.
9 And men were scorched with great heat, and blasphemed the name of God, which hath power over these plagues: and they repented not to give him glory.
10 And the fifth angel poured out his vial upon the seat of the beast; and his kingdom was full of darkness; and they gnawed their tongues for pain,
11 And blasphemed the God of heaven because of their pains and their sores, and repented not of their deeds.