Who is responsible for the Rwandan Genocide?

A friend and I were having a friendly debate the other day about who was responsible for the Rwandan Genocide. We both agree that no one group can be blamed for the genocide, but we primarily put the blame on two different groups. My position was that the Genocide was primarily the fault of the Belgian colonizers, who divided and angered a previously fluid and docile society. My friend said that it was the fault of the Rwandans, as they were the ones who decided to kill each other, rather than do something peaceful, similar to what South Africa did after apartheid.
Eventually, we agreed to disagree after we realized that we were just repeating our positions to each other in slightly different ways.

I was wondering what Fluther thought; should we hold the Belgians responsible, or should we hold the Rwandans themselves responsible for not working out their differences peacefully in a manner that other countries have done in a similar situation?

Finally, I would like to say that no one group is to blame for this, and casting blame now is useless. It is not important who is to blame, what is important is that the genocide happened, and that fact cannot be averted. I just want to know what other jellies think on this debate.