Q - How will the tribulation begin?

A - The tribulation will start when the Antichrist signs the seven-year peace agreement with Israel.

Because there have been several major peace treaties signed between Israel and her Arab neighbors, it's important to look for one that will allow Israel to rebuild the Temple, which was destroyed in 70 A.D.

And he (the antichrist) shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of abominations he shall make it desolate, even until the consummation, and that determined shall be poured upon the desolate (Dan. 9:27).

Remember the Rapture takes place before this happends!