From the article in dianavan's link...

"This wealth of information creates a new picture about what is motivating suicide terrorism. Islamic fundamentalism is not as closely associated with suicide terrorism as many people think. The world leader in suicide terrorism is a group that you may not be familiar with: the Tamil Tigers in Sri Lanka.

This is a Marxist group, a completely secular group that draws from the Hindu families of the Tamil regions of the country. They invented the famous suicide vest for their suicide assassination of Rajiv Ghandi in May 1991. The Palestinians got the idea of the suicide vest from the Tamil Tigers.

TAC: So if Islamic fundamentalism is not necessarily a key variable behind these groups, what is?

RP: The central fact is that overwhelmingly suicide-terrorist attacks are not driven by religion as much as they are by a clear strategic objective: to compel modern democracies to withdraw military forces from the territory that the terrorists view as their homeland. From Lebanon to Sri Lanka to Chechnya to Kashmir to the West Bank, every major suicide-terrorist campaign-over 95 percent of all the incidents-has had as its central objective to compel a democratic state to withdraw."