The novel begins in the year 1805 during the reign of Tsar Alexander I and leads up to the 1812 French invasion of Russia by Napoleon. The era of Catherine the Great (1762–1796), when the royal court in Paris was the centre of western European civilization, is still fresh in the minds of older people. Catherine, fluent in French and wishing to reshape Russia into a great European nation, made French the language of her royal court. For the next one hundred years, it became a social requirement for members of the Russian nobility to speak French and understand French culture. This historical and cultural context in the aristocracy is reflected in War and Peace. Catherine's grandson, Alexander I, came to the throne in 1801 at the age of 24. In the novel, his mother, Marya Feodorovna, is the most powerful woman in the Russian court.
War and Peace tells the story of five aristocratic families—the Bezukhovs, the Bolkonskys, the Rostovs, the Kuragins and the Drubetskoys—and the entanglements of their personal lives with the then contemporary history of 1805 to 1813, principally Napoleon's invasion of Russia in 1812. The Bezukhovs, while very rich, are a fragmented family as the old Count, Kirill Vladimirovich, has fathered dozens of illegitimate sons. The Bolkonskys are an old established and wealthy family based at Bald Hills. Old Prince Bolkonsky, Nikolai Andreevich, served as a general under Catherine the Great, in earlier wars. The Moscow Rostovs have many estates, but never enough cash. They are a closely knit, loving family who live for the moment regardless of their financial situation. The Kuragin family has three children, who are all of questionable character. The Drubetskoy family is of impoverished nobility, and consists of an elderly mother and her only son, Boris, whom she wishes to push up the career ladder.
Tolstoy spent years researching and rewriting the book. He worked from primary source materials (interviews and other documents), as well as from history books, philosophy texts and other historical novels. Tolstoy also used a great deal of his own experience in the Crimean War to bring vivid detail and first-hand accounts of how the Russian army was structured.
The standard Russian text of War and Peace is divided into four books (fifteen parts) and an epilogue in two parts – one mainly narrative, the other thematic. While roughly the first half of the novel is concerned strictly with the fictional characters, the later parts, as well as one of the work's two epilogues, increasingly consist of essays about the nature of war, power, history, and historiography. Tolstoy interspersed these essays into the story in a way that defies previous fictional convention. Certain abridged versions remove these essays entirely, while others, published even during Tolstoy's life, simply moved these essays into an appendix.