I stumbed across a documentary that referenced the Spanish Civil War and how people from all over the world were motivated to travel to Spain to fight the fascists. This was a war of ideology. They were either communists, or simply anti-facists, but believed in the struggle enough to fight for it.
http://en.wikipedia.org/wiki/International_BrigadesThis is the strongest parallel I've seen to the Islamic Jihadist movement. A movement, who in its most general form wants foreign influence out of muslim lands.
