That's the title of the new and excellent Dominic Lieven book and the subtitle is The True Story of the Campaigns of War and Peace. Excerpt:
In many ways the greatest hero of the Russian war effort in 1812-14 was not a human being but the horse. To some extent this was true of all European land warfare at that time. The horse fulfilled the present-day functions of the tank, the lorry, the aeroplane and motorized artillery. It was in other words the weapon of shock, pursuit, reconnaisance, transport and mobile firepower. The horse was a crucial — perhaps even the single most decisive — factor in Russia's defeat of Napoleon. The enormous superiority of the Russian light cavalry played a key role in denying food or rest to Napoleon's army in the retreat from Moscow and thereby destroying it. In 1812 Napoleon lost not just almost all the men but virtually all the horses with which he had invaded Russia. In 1813 he could and did replace the men but finding new horses proved a far more difficult and in the end disastrous problem.
Lieven's earlier Empire: The Russian Empire and its Rivals is one of my favorite non-fiction books.