I'm not going to argue the toss with you, but you've got the stress wrong on a number of things there. One is that Darby (who died around 1880) founded something called "premillennial dispensationalism" as a movement, when it's the name of a doctrine held by the movement he did found, the Plymouth Brethren. Another is to think the Plymouth Brethren are only American when they were first Irish and British (there are still PBs in the British Isles). Another is to consider this Christian splinter group as a completely new religion like Mormonism, which is a great overstatement. Most of all, though the influence of dispensationalism was considerable, you're mistaken to consider that modern Evangelicalism derives from it in the mechanical way you describe. Modern fundamentalist eschatology is hugely influenced by it, but in many other ways modern Evangelicalism does draw on an older tradition that can at least be partly traced back to the Puritans (who, btw, did not all up and leave England for the New World), and certainly to the revivalist movements of the C18 and C19.