In War and Peace there are no two ways about it: war is a brutal, savage, animalistic thing that goes against human reason. Tolstoy is horrified by the idea that the disagreements of a few people in government are solved by the movement of thousands of men across hundreds of miles, mostly to kill and be killed in turn by other men. Every battle is described as chaotic, having nothing to do with strategy or planning, grisly, and usually not even useful in determining a winner.
Although this is probably not Tolstoy's intention, his "history textbook" insertions disrupt the narrative and place the reader at too much of an emotional distance from the characters.
Francois Truffaut said that it's impossible to make an anti-war movie, because any time you show fighting on the screen you can't help but glorify it. This holds true for War and Peace, because even though it is a deeply pacifist book, by far and away the most exciting passages are the ones depicting battle.