It's actually going to be a lot more important for you to read it than to speak it, and as an above poster has suggested, the language has changed some over the last 150 years and you may need to know both traditional and simplified characters. I don't think anyone will expect you to be fluent in it to study the history, and you might be able to get away without it, but if you can't read materials in the original language but only things that have been translated, you're going to be very limited in your choice of research topics and won't be able to do the cutting-edge stuff that hasn't been studied. Most PhD programs require you to acquire reading knowledge in a foreign language anyway (and often several), no matter what your subject, so you might as well take some Chinese language classes.
You can do that while getting the PhD; a couple years should be enough to get by with a dictionary (although Chinese bilingual dictionaries are hard to use! Ask your Chinese teacher to explain ... more.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.