I am not looking for someone to write the thesis for me, just discuss possible ideas.
I know what you mean, it's okay! This sort of thing can SEEM difficult, but it is not.
You are being asked, "What is the book about?" But if a whole book is necessary for explaining the message, it sure is a tough challenge to express that message in a single thesis statement.
But when you look at a review online, you get the answer right away. Google this: review, gordon, postwar japan as history
Look at a review, and meditate on the key words in the introduction. Look at what the 3 themes are that I see mentioned in some review.
You are going to need to get very good at succinctly expressing the message of an article or book. You can always find it in the introduction!