Remember that with theme, you have to be careful to not just present a topic, so avoid a one-word response like "intolerance" or something. One word = Topic, not theme.
Usually instructors want to see a theme statment, which should be a complete sentence that is universal about life. On the other hand, short phrases tend to be viewed more as thematic ideas. Both are ok in different contexts - just make sure you know what is required from your instructor.
Just never use a topic, which is broad and usually just one word.
A theme statement might look something like this: "The horrors of war may strip the spiritual beliefs from even the most devout of followers" - since there is a recurring message of God being "dead" in the book.
A thematic idea could be "The importance of family"
A topic would be "Genocide"