The Japanese particle 'wa' (は) it typically called the topic particle. It indicates a topic, and then subsequent sentences refer to that topic in some way (the topic may be the subject, object, or some other case in the following sentences).
However, that is not the true meaning of the particle. What it actually is is an emphasis particle - it emphasizes some word or phrase. It's only by convention that it's come to be used to indicate the topic, and at times it's also used for other things.
So really, it's like "War! What is it good for?"