Isaiah Berlin's essay The Hedgehog and the Fox was his most popular essay. It was meant as an "intellectual game" in which he expands on an old Greek fragment written by Archilochus: "The fox knows many things, but the hedgehog knows one big thing."
Berlin defines a possible meaning, and then expands on Leo Tolstoy's theory of history, which he wrote about extensively in lengthy digressions in War and Peace.
Berlin divides some of the great writers and thinkers in history into two groups: hedgehogs and foxes. The Hedgehog knows one big idea, which would likely be some kind of philosophical ideology, and seeks to understand the world fitting his or her conceptions through that lens. The Fox holds many different views, some of which are likely contradictory, contextualizing on many different levels.
Tolstoy did not like the historians of his time, believing them to focus on the "leaves of the tree" while they should be focused on the roots. His focus on history likely grew out of a life long search for truth, and a belief that history should follow empirical evidence. He was very interested in cause and effect from a very young age.
Leo Tolstoy was paradoxical, and his philosophy of history had errors that are easily identified, even as he masterfully painted Napoleon's invasion of Russia in his epic War and Peace through this philosophy. "The conflict between what he was and what he believed emerges nowhere so clearly as his view of history," Berlin wrote, "[his philosophy of history] to which some of his most brilliant and most paradoxical pages are devoted."
Tolstoy took the "French encylopediasts" at their word, and tried to study social behavior "as one might study a beehive or an anthill." That is, relying on empirical data, and looking for a clear, concise and simple empirically based scientific method. This tendency stuck with him, even later in life when he rejected his earlier works, and became much more religious. He continued to preach simplicity, and believed "man suffers much because he seeks too much."
Berlin posits that amidst all these paradoxes, Tolstoy was a Fox that believed in being a Hedgehog, and really shaped his own paradoxical philosophy through his attempts at being a Hedgehog. It is a short book, or long essay, at 90 pages, and worth reading if you have an interest in either Leo Tolstoy or the philosophy of history. You may also want to read Tolstoy's essays in War and Peace, as Berlin doesn't spend too much time elaborating on Tolstoy's core message in the essays which was a rejection of the "Great man" view of history.