Why did Osama bin Laden declare war against the US?

Answer 1

Osama bin Laden declared holy war (Jihad) upon the US for what he described as "defamation", "desecration" and "destruction" upon his middle-eastern neighbors.

Osama himself was originally a businessman hailing from Saudi Arabia, and when the Soviet Union invaded Afghanistan to secure oilfields, it was the western powers actually SUPPLYING the insurgency (mujahideen), because they were so desperate to stamp out Communism.

If you are American you would probably at this point be shouting a lot of patriotic drivel at me, (or rather typing it in capital letters), but if you understand Islam, you would know that invading a holy country, in a radical Muslim's eyes, is about as close you can get to slapping the prophet Muhammad (blessed be his name), across the face.

So no, it wasn't because he was a "crazed Islamic radical who was very wealthy", it was because he was a paranoid, overly-zealous extremist who had a view that Islam is the only religion that should be in the world. Everyone who was not Islamic was an infidel and therefore must be converted or suffer the wrath of Allah.