Tolstoy is the God in War and Peace. He has opinions on everything and always finds strong evidence to his opinions. But those evidences aren't always true or effective.
For example, in chapter one of book eleven, Tolstoy argues that great men don't exist, because "the sum of human wills produced the Revolution and Napoleon, and only the sum of those wills first tolerated and then destroyed them"(Tolstoy 732). Tolstoy thinks that Napoleon is not influential, for he alone can never cause the war. According to Tolstoy, Napoleon appeared as a conqueror when the war happened, just like cold wind blows coincidentally when oaks are budding. Cold wind does not influence the budding of oaks, so Napoleon was not influential to the war.
However, a conqueror was very essential for the war to occur. Tolstoy came up with a untenable argument because his example of cold wind and oaks does not have the same nature as Napoleon with respect to the war. Oaks are budding in late spring; during that period of time, cold wind happens to blow. Cold wind is neither necessary nor sufficient for the oak to bud. Yet a war couldn't happen if there wasn't a conqueror. No one can imagine a war without a conqueror who makes decisions and leads the army. That is, the existence of a conqueror, in this case Napoleon, was necessary for the war to happen despite the fact that Napoleon as an individual didn't guarantee the occurrence of the war. DOESN'T IT MAKE A GREAT MAN IMPORTANT?
And at last, I have a few points to clarify. First, I'm not denying the influence of "the sum of human wills"(Tolstoy 732). Napoleon became powerful not only because of his abilities and luck: all the objective condition, such as social environment and public opinions favored his revolution. Second, I'm not focusing on Napoleon's importance as an individual. The existence of great men, not the great man himself, is important. He could be Napoleon, or anyone else with similar "greatness"in him. There is a mutual relationship between history and great men-- the development of history awaits great men to rise; great men plays a important role in almost every turning points of history.
* I didn't have a chance to have someone proofread this, so please don't mind my wording and grammar problems. And feel free to comment below if there's certain phrasing that you don't understand.