OK, before we start unpacking the title, let's everyone take a deep breath. Relax. Imagine being in a happy place. Forget that this is War and Peace, the gold standard for long, complicated, classic novels. None of that will help us actually deal with the text at hand, so let's just throw all that stressful baggage out the window before thinking – really thinking – about the title.
When you get right down to it, this title is about as WYSIWYG (what-you-see-is-what-you-get) as it gets. "War" and "peace" are two words that cover a lot of ground – the whole scope of human history in fact. Tolstoy tries to encompass as many ways of thinking about these two concepts as possible.
For war, we've got graphic descriptions of the kind of hand-to-hand combat that went on during battles, descriptions of army and POW life, some pretty cool fictionalizations of real-life generals and politicians as they strategize the campaign, and finally a lot of deep-thought philosophizing about the nature of conflict and the morality of hordes of people killing other hordes of people.
For peace, we've got the tiniest and most trivial things that happen in the home (to the point of talking about poopy diapers at one point), love and romance and the way feelings come and go, social life in the upper classes, the feudal relationships between the aristocracy and the serfs, and the ways peace tends to creep in and take over war.
So yeah – those two little words cover quite a lot of ground.