The pre-tribulational rapture goes hand in hand with the dispensational notion of the Church and Israel. Darby had to invent the pre-trib rapture to fit with his radical views on Israel. According to his theory, the Church needs to be raptured out of the way so God can once again begin dealing (pouring out His wrath) directly with national Israel. Since the Church does not share in anything belonging to Israel, including wrath, they must be removed. This is all their theory.
And so they needed to search the Scripture to find something that would fit these views. Their eyes landed on 1 Thess. 4:16,17 as justification, even thought it plainly says nothing about a pre-trib rapture. The system comes first.
This is simply not so! Rev. Morgan Edwards included a discussion of the pre-Trib rapture in his book "Milenium, Last Day Novelties" written in 1788 (some 40 years before Darby). He claimed that he had written the same thing in 1742, but I have not been able to corroborate this statement. Joseph Mede (1586-1638)also was a pre-trib scholar. Grant Jeffrey, a current prophecy scholar, discovered an apocalyptic sermon written sometime between 565 and 627, attributed to the Syrian church father Ephrem of Nisibis, describing a pre-trib rapture. Even earlier, Victorinus, Bishop of Petau, wrote in 270:"these shall be in the last time, when the church shall have gone out of the midst" referring to the judgments during the tribulation. You can argue Bible verses, but don't tell me that a pre-trib rapture is Darby's invention because it had been taught for centuries!