It's called Islamic Fundamentalism, and it's not the leading cause of it all.
Only 2%, at most, of all Islamic Fundamentalists are violent and/or terrorists. When someone is an Islamic Fundamentalist, it just merely means they have a strict interperetation of the Qoran. For example, it says somwhere in the Koran, I think, that the woman's place is to work at home, or something along those lines. Islamic Fundamentalists take that to heart and do not allow their women to leave the home. At all. The 2% of the people who do use terrorism wo just so happen to be Muslim take the 'defend your religion' part way too far and believe in terrorism as a holy way to defend their religion, when, really, Islam has nothing to do with any of it, most of the time. Hence, jihad usually becomes an issue with which to be dealt.
Really, the thing with Islamic Fundamentalists is they just use the Qoran as an excuse to commit acts of terror against others, especially in the Israeli-Palestinian conflict. The Palestinian Islamic Fundamentalists basically say that the Jews have occupied the lands that do not rightfully belong to them, but the Palestinians, and they use this as an excuse to defend their religion and use acts of terror to create the problems the Middle East faces, today.
"Do or do not, there is no try" -Yoda