That a select group of rich families are secretly running the US is a theory.
That the Depression happened on purpose is a theory.
That people were forced to give up any gold they have isn't a theory, it's false; people still have gold rings, necklaces, etc.
That the sinking of the Lusitania was ordered by banking families to make a profit is a theory.
That those banking families sold fuel to Germany in WW2 is a theory, and an unlike one at that.
That Hitler used communism to sell war to the public is a half-theory. While fear of communism helped him get power it was nationalism and restoring honour that sold the war to the Germans.
That the current economic troubles is designed to dismantle economies is a theory.
That 9/11 was an inside job and that explosive were used is a theory.
I will agree that there's a big difference between these theories and history.