What am I going to write about?
Many disciplines, among them the humanities and the social sciences, do not prescribe dissertation topics but leave instead the choice to you. Your academic advisors in most cases will hesitate to press you in one direction or the other. You should be well aware of the fact that you will have to deal with the chosen issue a couple of years, and that you need a lot of energy (and joy) to master it. Make sure that your scientific background and knowledge are solid enough to cope with arising difficulties: to learn a new language in order to read relevant texts or to acquire new methodological skills from the very beginning takes time and is laborious. Most likely, it postpones the completion of your work considerably. Along with it comes stress, and your financial risk is heightened enormously if the end of your working contract or grant approaches far earlier than you can hope to submit your thesis.
Do not ignore these considerations and do not think them minor to your research questions. On the contrary, try to bring up these issues in discussions with your academic advisors as soon as possible. Scientific ambition is prerequisite, hardly less important however is to keep your work feasible.