Back to the original question...
As has been pointed out already in this thread, the pre-tribulation rapture is an aspect of dispensational theology. If you believe in a pre-trib rapture, you are espousing dispensational theology whether you realize it or not, or whether you understand it or not.
As with so many other doctrines, the groundwork is laid though conclusions based on a lot of study, put forth by Bible teachers, and believed by those who they teach. This is true of other theological systems as well - not just dispensationalism.
While Darby and Scofield have been instrumental in popularizing dispensationalism, in my opinion it was really Lewis Sperry Chafer who systematized it. If you really want to understand dispensationalism, read his Systematic Theology, especially the volumes on Ecclesiology and Eschatology (he starts to lay it on hard and heavy in the Ecclesiology volume - it would be better to read that before the Eschatology volume).
The bane of systematic theology is its use of proof-texting and its reliance - especially in discussions such as this - on small "sound bite" (or maybe we should say "word byte") arguments.
As far as Scripture to support the pre-trib rapture, I would recommend a study of the epistles to the Thessalonians. Also, compare what Jesus said in His "Sermon on the Mount" and the "Olivette Discourse" (Matthew 5-7 and 24-25) to what He said in His "Upper Room Discourse" (John 14ff). Those are key passages that Chafer uses to show that there is a distinction between Israel and the church.
Time and space do not make it practical for me to go much more into it. But seriously, if you want to understand dispensationalism, read Chafer. If you want to understand reformed or covenant theology, read Hodge or Berkhof. They can explain their positions much better than I can in such a brief post.
I know that sounds like a lot of work, but it is rewarding work. In the end, the important question is, which system - if any - best takes into account the whole body of revelation? I have concluded, for the present time at least, that it's dispensationalism (although there are aspects of dispensationalism that I reject). You may come to different conclusions.
All the best to you...
Rusty Sword