Greetings!
If I understand the assignment correctly, you are to come up with a theory (or find one in your research) which helps to explain why the genocide was not prevented. In that case, I would think that you would propose that theory as a possible solution, that is, an answer to the question, and show why that theory does or does not explain what happened. You would probably just want to use the one theory as your main argument; however, you could, if you wanted, present other theories and tell why they are not workable. It probably depends a lot on how long the paper must be. If you need to fill out ten pages, you will probably need to touch on more reasons/theories than if it is only a five page paper.
I hope this helps!
Thanks,
Sarah, EssayForum.com