The significant military engagement that marked the conclusion of the Napoleonic Wars in 1815 was the Battle of Waterloo. This decisive battle occurred on June 18, pitting the forces of the British-led coalition against Napoleon Bonaparte's French army. The defeat of Napoleon ended his rule as Emperor of the French and ushered in a period of relative peace in Europe known as the Congress of Vienna. Waterloo's outcome reshaped the balance of power in Europe and established the groundwork for later international relations and alliances.