Who is to blame for these atrocities in Rwanda?

I believe that in the case of the Rwandan Genocide the Hutu, Tutsi, UN, and Belgian people are to blame.
The Hutu are to blame because the Hutu extremists were the ones who actually perpetrated such terrible deeds. The Tutsi are the ones to blame as well, because they ticked off the Hutu, by forcing the Hutu with sanctions, menial labor and a feeling of perceived superiority compared to the Hutus. It's like if you keep slapping a dog eventually the dog will bite your throat and rip it out.
     Of course the Belgians should take blame as well seeing that they started everything by taking over the land and favoring the Tutsis which would cause racial tension for generations to come. But the people who are truly disgusting in their hypocrisy and blame, are the United Nations. The UN was started to keep the world at peace and to stop any further genocides. BUT yet AGAIN the UN simply SAT BY and WATCHED the DESTRUCTION of the TUTSIS AND THE HUTUS. And what did they do? NOTHING!! ONCE AGAIN THEY SAT BY AND REFUSED TO LIFT A FINGER FOR THEIR "FELLOW MAN". But I don't blame the Americans, because I can see their fear in another Somalia incident. But not the UN the UN sucked at the Rwandan Genocide.