Aren't Wars Started By Religion?

People are sometimes skeptical of Christianity (or any religion) because they feel that many wars are started in the name or religion and that the world might just be a better place if there was no religion.

There is no doubt that many bad things have been done by religious people. However, the Communist Russian, Chinese, and Cambodian regimes of the twentieth century all rejected belief in God but produced massive violence against their own people. So clearly not all wars are caused by religion. Societies that have rid themselves of all religion have been just as oppressive (and sometimes even more) than societies that seem to be religious.

The only real common denominator behind all wars is people. So the only correct conclusion we can come to is that there is some violent impulse inside people regardless of their religion. This conclusion makes sense when viewed from the Christian worldview which says that every person is born sinful and will have a natural propensity to do wrong and needs to repent of this and trust Jesus for salvation and then beginning living out the peace, justice, love, service, etc. that is taught in the Bible.