I'm agnostic re aliens. 50/50. If one taps me on the shoulder right now I won't be shocked. I'll be scared shitless, but I won't be shocked. Hopefully I would have the nerve to kick it in the balls, beat it unconscious, and get it to the nearest Emergency Room sans interstellar retribution. I would offer it to Texas A&M in exchange for Permanently Endowed status.

No problem with Roosevelt's allowing Pearl Harbor. We had the Japanese naval code deciphered. This is a conspiracy that could have been carried out by a small handful of people.

I do not believe in conspiracies that would take hundreds of people to carry out and/or cover up. I'm guessing that 1 perpetrator in 20 would ultimately spill the beans. This rules out most of the hypothetical conspiracies on your list.

JFK is fishy as hell because of one indisputable event: Jack Rubenstein kills Oswald on live TV. The whole thing reeks. I do not believe the government killed Kennedy. I hold similar to the findings of the BBC who made a very good documentary in 1989: Kennedy enlisted the American Mafia to kill Castro; Castro caught the hitmen in Cuba; Castro says, "OK. He's offered you $10 Million [???] to kill me; I'll give you $10 Million and One [???] to kill him." The government was shocked by the assassination and scared shitless by the propsect of the public's finding out that Kennedy was in cahoots with The Mafia. Or something along these lines. Murder? No. Cover up? Plausibly.

The whole Jews stabbing WWI Germany in the back thing has been blown out of proportion. It wasn't the Jews explicitly. The industrialists of Germany got tired of going further into debt to government IOU's. A lot of these were Jews; most were not. It just happened to be convenient for Hitler to blame the Jews and not the Fat Cats in general.