Truth about the Tribulation

When I was in High School in the early 1960s, I was taught there was nothing more that needed to happen before the rapture of the saints and that the tribulation could come at any time. If that was the case, what was God waiting for? So my wife and I have read many books on end time events since we were married. But they all seemed to repeat what I learned in high school. So there is a great thing...