In volumes I and II, the peace parts and the war parts are separate. From chapter III, they no longer are- when Napoleon invades Russia. There's more history, and more philosophy.
That reminds me of Flaubert's comments on War and Peace in a letter to Turgenev:
"Thanks for having me read Tolstoy's novel. It is 1st rate! What a painter and psychologist! The 1st 2 volumes are sublime, but a 3rd goes downhill terribly. He repeats himself and he philosophises. One sees finally the author and the Russian, and up to then one saw only Nature and Humanity. At times, it seemed to me there were things like Shakespeare's. I cried out in admiration while reading- but it is long!"(http://books.google.no/books?id=NV1m9zDBWyIC&lpg=PA26&ots=OvjiEzHm76&dq=flaubert%20turgenev%20letters%20painter%20psychologist%20philosophizing%20war%20and%20peace&pg=PA26#v=onepage&q=flaubert%20turgenev%20letters%20painter%20psychologist%20philosophizing%20war%20and%20peace&f=false)
Place War and Peace next to Anna Karenina, it's difficult to pick- War and Peace has greater scope and grand scale, covering a long period with a lot more characters in many places, Anna Karenina has a smaller focus and therefore greater psychological depth. The latter is also tighter and, I think, more artistically perfect.
E.g: Why does Pierre run into Dolokhov whilst going around to see the soldiers? Why does the wounded Andrey end up next to his rival Anatole in the military hospital? Why is he taken to the Rostovs? Why do the Rostovs, on their way out of Moscow, run into Pierre?
Less problematic: Why does Helene ask for a divorce when Pierre has fallen in love with Natasha, hence she makes it convenient for him to marry someone else? etc.
Of course, if one examines all great novels and questions the events logically, there would always be something unnatural, unconvincing, contrived or merely functional (such as the functional deaths in Jane Austen's novels, according to Nabokov, which do nothing but move the story forward). Even Flaubert's Madame Bovary, often called a perfect novel, has some impossibilities, as pointed out by Nabokov in his lecture. The question is whether it is so obvious that it disturbs the reader (such as in Jane Eyre, Jane leaves Rochester and ends up at the least possible place- her cousins' home, and later returns to Rochester to find the path cleared of all obstacles).
Such issues in War and Peace do bother me a bit, but there are so many marvellous things that these imperfections can be tolerated.
Take the scenes right before and after the old prince Bolkonsky's death. For years, the interactions and relations between him and his daughter Marya are the same- he abuses her, terrorises her whilst she endures his temper and by doing so prides herself in her own self-sacrifice, he doesn't become nicer, she doesn't become stronger. Suddenly, the approaching death, with the awareness of it, brings about a change, some kind of epiphany. The old prince realises he has wronged his daughter, but more interesting is what goes on in Marya's mind, from worry and fear to relief and the wish that her father will die and free her from torment, followed by shame, guilt, bad conscience, then sorrow, grief and lack of interest in all things. But the situation doesn't allow her to grieve for long. She must stand up and take care of practical matters, and her reaction in such a time of lonesomeness and despair is to try to think like her father and brother, and to act like them (though she doesn't have their decisiveness and authority). It isn't because of her sex, but rather, her personality- under the same circumstances, Natasha would act as herself instead of pretending to be someone else, and have greater authority. One can see that in a later chapter, when Natasha helps with the packing for her family.
Now consider Andrey. I've written before that he's disillusioned twice- with marriage and with military life. He's disillusioned a 3rd time, when he falls in love again and once more finds life worth living and everything with meaning. Each time, he suffers, because he always runs away- the 1st time, into the army, the 2nd time, to the country and the 3rd time, again to the army. And the 3rd time is worst, he suffers a great deal to the point that he can't bear meeting anyone from the past, as though his life's divided into 2 parts, with and without Natasha. All the descriptions of his meeting with Pierre are sublime.
These passages are magnificent.
Concerning the philosophising, although I'm more interested in the people and their relationships, I'm fine with it, unlike some readers including Flaubert. 19th century people weren't used to it, but such a mix of genres can be found in postmodern literature, Tolstoy's ahead of his time.
I'll write more about War and Peace and Anna Karenina.