I remembered that War and Peace was a vigorous assault on the "Great Man" theory of history: the idea that Napoleon (and other such important historical figures) had, through his inherent genius, altered the course of history and directed the fate of nations.
What I'd forgotten was that the last section of the book is also a vigorous assault on the idea of free will.
The great thing about Tolstoy is that he always convinces me, at least for awhile. Doesn't matter what he's arguing. He might be saying Shakespeare is bad, or that all art is worthless, or that Napoleon was a nobody, and it doesn't matter, because I will believe him. He's just that convincing.
Of course, it's not that hard to disbelieve in free will. I daresay that anybody who thinks about it even a little bit must shortly conclude that free will either doesn't exist or is meaningless. Either we do things for a reason (in which case that reason determines our actions) or we do them at random (in which case our will is free, but a little terrifying). So yeah, this book was a good reminder: oh yeah, I don't believe in free will.
Like most of Tolstoy, the insights you get don't lead anywhere. This is a common theme in his work. You gain some mystical insight, but it either fades or it doesn't matter. Ivan Ilyich experiences a moment of revelation, but he still dies screaming. Levin realizes that peasant simplicity is the key to life, but he's rapidly distracted from it by the exigencies of his position. Pierre Bezubhov starts to listen to the voice of moral intuition inside him, but he's brought back to merely human concerns by his love for Natasha. In Tolstoy, all consolation is temporary. You dip into this well of consolation whenever life becomes too unbearable, but eventually you have to go back to real life.
Similarly, the realization that there's no free will can have little effect on your life. Yes, my will isn't free, but so what? I'm still going to do the things that I do.