I've only skimmed http://en.wikipedia.org/wiki/History_of_democracy
but it's pretty interesting stuff, it's where I get my "centuries" comment from. As for "conquest," I don't want to argue the creation of an "American Empire". I'm not qualified for those kinds of debates, although I suppose "conquest without domination" is pretty much how the British Empire ruled most of their colonies from what I know. Could argue that with the establishment of strong military positions that Iraq and Iran are "colonies".
Anyway, I doubt the founding fathers and the resulting US Civil war were in a position where they could have offed the leaders of the opposing side. Intelligance was far too slow, but nowadays, it's so common for people to dissapper, it's unusual for people to protest.
And to loop back to Star Wars, well, ultimately, the whole thing is a ruse, but in response to your WW2 leader comment, nowadays, the media has more power in British politics than our own politicians. I feel the "ex-colonisers" need some more money in their pocket IMHO. Where's Grievous when you need him!