The classic conspiracy theories I've read are often interesting, but ultimately I find them unconvincing. They all have logical flaws, questionable evidence, require too many people to keep too many huge secrets for too long, or some combination.

My personal favorite is a niche one, often called Hitler at Pasewalk and apparently debunked. But I want to believe! QRD: Hitler was a loser with no leadership ability who was temporarily blinded by gas at the end of World War I, then went blind again when Germany surrendered. A psychologist named Edmund Forster cured him with hypnotism, but his "you are special and have a destiny for Germany" message went tragically wrong.

I think the biggest conspiracy theory in American history is going on right now. I believe the election was stolen for Biden by a combination of corrupt and/or compromised Democrats (and some Republicans) who are (to some degree) controlled or supported by hostile foreign powers like China, Venezuela, and Cuba. That would explain many odd and extreme behaviors on both sides. I think it means incredible drama, and probably violence, between now and inauguration day (and maybe after). I think Trump is on the side of justice and the USA, and I think he'll triumph, but it won't be pretty. The world will be a different place in five weeks.