From 1812 to 1815, the United States was at war with Britain. Officers and sailors, having developed deep animosities during the preceding decade over issues like impressment, fought each other with patriotic rancor. Yet, a few years after the end of the war American and British sailors and marines were sailing together to eliminate the piracy and maritime insecurity that dominated the region during the wars for Spanish-American independence. This rapid diplomatic reversal, from enemies to partners, offers an interesting history of diplomatic change following war. These post-conflict relationships were affected by the perception of power imbalances, the importance of aligning national interests, and the diplomatic role of non-State Department entities like the US Navy. This history speaks to the character of the Anglo-American relationship in the nineteenth century, oscillating between friends and foes, and illustrates the political and economic connections within the maritime and diplomatic past.