The great tribulation began nearly two thousands years ago

They have preached that Jesus first will come invisibly for the
world and take God's people to heaven. After that the Antichrist
appears, and the great tribulation will begin and last for seven
years. Then Jesus shall come to judge the world. This is only a
theory and it does not agree with the Bible.

As it was in the days of Noah, so also it will be in the days of
the Son of Man. When Noah went into the ark, the flood came
and destroyed all. Likewise, as it was in the days of Lot. The
day Lot went out of Sodom, it rained fire and brimstone from
the heaven and destroyed all. According to those things, it will
be in the day the Son of Man is revealed. Luke 17:26-30.

When Noah went into the ark, it was no delay of seven years
before the flood came. The flood came the same day. On the day
Lot went out from Sodom, it was no delay of seven years before
the fire fell above Sodom. It happened the same day. Of this we
can understand, at the same day Jesus comes to take his people
to heaven, then God's judgement comes at once above the
ungodly world.