Conspiracy theories

Overview

This page is a list of known conspiracy theories. For discussion of the idea itself, see conspiracy theory.

Issuepedia:Rampant Paranoia: theories we aren't taking seriously, given the current evidence
Manchurian Candidate scenario: subornation of a high-level official by malign foreign interests

9/11 anomalies: not so much a theory of what as pointing out that the official story has holes you could pilot a plane through
- Bushco engineered 9/11: extrapolating the evidence to one possible (but unproven) conclusion
global warming denial often takes the form of arguments for the existence of a conspiracy between international scientific organizations, the environmental lobby, the green industry, and Western politicians

Queries:

Are there any major tragic events since approximately 1900 for which no popular "conspiracy theory" exists?
Why are there so many conspiracy theories?
What is the approximate ratio of theories which remain unproven or disproven to those which prove true? Is there enough data to draw a curve of {likelihood that any given theory will be proven or disproven} over time? (What is the half-life of a conspiracy theory?) Are there any characteristics which make a theory more likely to be resolved sooner? Are there any characteristics which make a theory more likely to be found true when it is resolved?

Some conspiracy theories which turned out to be true and are now officially recognized (and are no longer called "conspiracy theories"):

The Iran-Contra affair [W]: Reagan traded arms for hostages while denying that he did so; there was also allegedly a global narco-terrorism network headquartered in the basement of the White House. (kudos: apostle_of_eris)
"P-2 in Italy was real. They didn't completely succeed in taking over the Italian government, but they did steal the Vatican bank; and though I'm skeptical that they poisoned a Pope, they did get away with murder." (kudos: apostle_of_eris)
"remember the Maine!" - more of an anti-conspiracy, where an accident was claimed as a provocation for war

2014/06/18 [L..T] Abu Khattala comes into sharper focus «The second [possibility] is that the suspected ringleader behind the Benghazi attack is in on the Benghazi conspiracy. Sure, the sheeple will resist, but don't you see it? The conspiracy is so broad, so all-encompassing, and so far-reaching in its scope, the White House has even gotten to Ahmed Abu Khattala, convincing an alleged terrorist to stick to the talking points.»
2014/04/04 [L..T] Flight 370 Was Remote-Hijacked
2014/03/22 [L..T] 9 Huge Government Conspiracies That Actually Happened "As the years pass, however, secrets surface. Government documents become declassified. We now have evidence of certain elaborate government schemes right here in the U.S. of A."
2014/02/21 [L..T] From the fringe to the Hill It's alarmingly common to hear congressional Republicans repeat some deeply odd conspiracy theories. But more often than not, the theories didn't start on Capitol Hill; they just ended up there.
2001/06/04 [L..T] Pearl Harbor: The Facts Behind the Fiction “Oliver Lyttleton, British Minister of Production, stated in 1944: "Japan was provoked into attacking America at Pearl Harbor. It is a travesty of history to say that America was forced into the war."”