Chamberlain wanted to appease Hitler because he thought Germany would form a buffer against communism expansion. He got to convince Daladier.
And here comes WW2

The US allied itself to Saudi Arabia also to fight against communism.
Unfortunately, Saudi Arabia isn't a democracy. 14 of the 19 9/11 terrorists came from Saudi Arabia.

The US got the Shah of Iran into power. And the Iranian population turned against him and kept americans as hostages for 444 days. And Iran is the first Islam-fundamentalist state, with its ideas spreading throughout pro-US non democratic countries.

The communist states collapsed in a domino effect (except Cuba and North Korea) in 1989-1991. Except for Romania, it was a peaceful revolution.

Marx considered religion as people's opium.
Communists don't commit suicide like religious fanatics. That's in large part why the collapse of communism was peaceful. Also, deterrence worked, because of the fear of death.
Deterrence doesn't work against fanatics. Look at Israel: they keep having victims from human bombs. Yet, Israel is so much more armed than Palestine.
The US is the most powerful and the most heavily armed country in the world and it can't stop religious based terrorism against its interests throughout the world.

Religious fanaticism or Communism: what's the most dangerous?

Raoul