I think many of the suggestions here fit your criteria of looking for a 'problem'. My own preference would be to look at Japan's isolationist strategy. The way you turn this into a 'problem', rather than just a description, is by framing the title of your assignment into a question. For example:
How successful was the Tokugawa shogunate's sakoku policy?
How far did society stagnate under the Tokugawa shogunate?
They both allow you to frame an argument/investigation rather than a description (in this case, looking at the efforts by the Japanese government to preserve existing social hierarchies, and whether Japanese culture and society thrived in defiance of those efforts).
Oh, and if you want a guide to writing history essays, here's
one I composed earlier.