All religions preach nonviolence. Every essential text, from the bible to the qu'ran preaches a nonviolent approach to life. Additionally, the idea of nonviolence is essential to the teachings of all religions. Hence, we today consider it simply natural that people shouldn't be violent because we were all brought up (rightly) being taught that violence is wrong and immoral. But we never question why is it natural that we should be so "naturally" against violence.
The answer comes from religion, and the origins of religion's anti-violence stance can be analyzed historically. During their early years, each major religion was a minority in the society in which it was created. As such, it was persecuted by the group in power. Each religion, consisting of a relatively small group of followers, could not advocate violence, because it would easily be crushed by the group in power. So nonviolence became the only manner in which a newly-founded religion could survive in the ancient world.
The key change occurs when that religion goes from being the persecuted minority to the religion of the those in power. The powerful members of that religion have to then re-adjust the interpretation of the basic nonviolent foundations of that religion. So religion becomes an excuse for violence. However, it is important to understand that it wasn't religion that caused the violence, it was the position of power. Religion does not necessarily promote violence-the attempt to either gain or solidify power does.
As we saw last week, religion is often used by powerful people to retain their power by violent means. However, religion certainly be used by those without power in a nonviolent manner to achieve social justice. People like Martin Luther, Gandhi, and the Dalai Lama are terrific examples of that...