This study investigates the reasons for the success of the Sixth Coalition against Napoleon in 1813. Four critical principles emerge from U.S. joint doctrine that provide a means to examine coalition warfare: national goals, unity of effort, strategic plans, and adherence to plans. These principles illuminate the importance of coalition warfare in the defeat of Napoleon. The failure of an earlier coalition, the Second Coalition in 1799, underscores the importance of the principles of coalition warfare to the success or failure of the coalitions against Napoleon and the French. This coalition failed because of its lack of attention to the details of coalition warfare. Its basic flaw, lack of a common coalition goal, undermined its unity and resulted in defeat. The development of a common goal, the liberation of Germany, combined with the decline of the French and reforms by Napoleon's opponents led to a level playing field in 1813. The 1813 spring campaign resulted in a stalemate. The coalition used the subsequent armistice to further improve both politically and militarily. These improvements, particularly the adoption of a unified military strategy, resulted in improved unity of effort and provided the Sixth Coalition the margin for ultimate victory.