Congress has formally declared war 11 times.

Spanish American War

The U.S. Constitution, ratified in 1788, gives Congress the sole power to declare war. Since then, the legislative body has formally declared war on another country a total of 11 times, during five separate conflicts. The first time was on June 17, 1812, against a familiar rival, Great Britain, nearly 30 years after the end of the Revolutionary War. A 19-to-13 Senate vote initiated the War of 1812, based on Britain’s alleged violations of U.S. maritime rights. Following that conflict, several decades passed before the U.S. declared war for a second time, in May 1846, initiating the Mexican-American War, a conflict over land rights that was caused in part by the U.S. annexation of Texas in 1845. Five decades later, on April 25, 1898, the Spanish-American War began with a declaration of war on Spain, just weeks after Spanish forces sank the USS Maine battleship in the harbor of Havana, Cuba. The war ended with the Treaty of Paris on December 10, 1898, and Spain lost its territories in the Caribbean Sea.

The U.S. then became involved in World War I after taking up arms against Germany in April 1917, and Austria-Hungary the following December. Although the Ottoman Empire, Bulgaria, and other nations joined the Central Powers, the U.S. only officially declared war against Germany and Austria-Hungary. A few decades later, the U.S. made six unanimous war declarations in two years, marking its entrance into World War II. Congress declared war on Japan on December 8, 1941, followed by Germany and Italy on December 11, 1941. Six months later, on June 4, 1942, Bulgaria, Hungary, and Romania were added to the list. Although the U.S. has been involved in numerous military operations around the world since the Second World War, 1942 marked the last time Congress officially declared war against another nation.

By the Numbers

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Key West “declared war” on the U.S. in the 1980s.

On April 23, 1982, the city of Key West declared its independence from the U.S. as a political stunt, calling itself the Conch Republic micronation. The move was made based on claims that the federal government was significantly disrupting the community with a new Border Patrol checkpoint (established to eradicate drug smuggling) that made the island’s thruway nearly impassable and hampered tourism. Key West Mayor Dennis Wardlow was named prime minister of the Conch Republic, and the self-proclaimed micronation “declared war” on the U.S., though it was more of a symbolic move than a violent conflict. Accounts written about the day’s events vary, but include protesters breaking a loaf of Cuban bread over a U.S. Navy officer’s head and attacking a U.S. Coast Guard cutter with water balloons and conch fritters.