I can imagine one of the reason why these wars begins is because of the different religions views. The religions have several guidelines and these guidelines are sometimes causing a mess. Like when someone draw the prophet Mohamed some Muslims get really angry cause it's against there religion to do that. Another thing about religions is that you become a part of a group, and as a group you stand a lot stronger then a single person. So when someone draw Mohamed, the Muslims get angry because they know they can. When you insult or argue about a religion you insult a group of people. It's much easier to start a war when you're already a gathered group.

So does people start the wars or the religion? Well, a religion consist of a bunch of people, so people start the wars, but mostly of the time because of the religions guidelines/views, and the fact that they together as a group are able to start the war.