War and Peace is classified as a Novel of Ideas, which are sometimes labeled as Philosophical Novels. Other examples are Voltaire's Candide, and all novels by Goethe and by J.-J. Rousseau. Of course, those three were all philosophers, while Tolstoy is primarily known as a novelist, but he did have his own philosophical perspective, particularly on the nature of history (see Trepanier on the second epilogue, in particular, since you mentioned it).
Much of War and Peace, as you know, is preoccupied with history, and as Tolstoy sets the principal characters in motion they tend to become caught up in forces much bigger than they are, even while their individual character traits influence their actions. To some extent, fiction is always grappling with the question of history.
Why? Because fiction--at least the novel and short story--are narrative art forms. And narrative means events exist in a sequence. As Aristotle famously said about the drama, it should have a beginning, a middle, and an end (not necessarily in that order). It sounds obvious, but think about what that implies: all narrative is necessarily a kind of history, in which the outcomes are a consequence of previous actions. What happens in the beginning affects what follows. So novels tend to display a theory of history, just because they rely on a narrative form.
Some are more self-conscious about this aspect of fiction than others, and Tolstoy falls into this category. You can view it, even, as a form of intellectual honesty: he is putting his cards on the table.
But I really like the way you phrase your question:
So I wondered whether this novel should be considered fiction, non-fiction or an amalgamation.
First, you accept that it is a novel, and you are even open to the possibility of it being a non-fiction novel (that's a genre that would become prominent in the twentieth century, with writers like Truman Capote and In Cold Blood). "Fiction" is easier to define than "novel," though, as the invention of a imagined reality which nonetheless is assumed to contain some truth about actual social reality. So fiction is quite different from "fantasy". And most of War and Peace certainly fits that definition.
Novels need not be uniform in their generic type. The Russian theorist of the novel M. M. Bakhtin argued famously that the novel is a combination of other generic forms, and that it has no generic identity of its own. He called it the "anti-genre" that comments on other genre forms: like journalism, science, cookbooks, and even philosophy. I don't remember if he used War and Peace as an example, but--as you noticed--it serves very well as a case study of just how multi-faceted a novel can be.