What should I do my research report on?

8th grade, I need to right a very in-depth research report on anything that I've studied in the past 2 years-- that's basically world history after the fall of Rome (including the Aztecs, Asia, religion, etc.) and American history up to Reconstruction of the Civil War (but I don't want to do American history). Things I have in mind are Buddhism, Renaissance, Aztec religion, and heresy in the Middle Ages, but I'm open to anything that you recommend! So, what do you recommend!? I have to choose by tomorrow!