On this day in 1779, the Louisiana governor and Spanish military officer Bernardo de Galvez, with the aide of American troops and militia volunteers, captures the British post and garrison at Baton Rouge, located in what was then British-controlled West Florida.
In a cunning and brilliant move, de Galvez included in the terms of the British surrender of Baton Rouge that the British also surrender Fort Panmure at Natchez to Spanish control. Defeated and on the verge of utter annihilation, the British had no other choice but to accept the terms.
The Spanish capture of Baton Rouge and Fort Panmure ended British control of the Mississippi Valley and opened the Mississippi River to a Spanish supply line—running from the Gulf of Mexico to the Ohio Valley--that greatly benefited the American cause. De Galvez was then able to lay siege to the British-occupied city of Pensacola, Florida, in the spring of 1781, which ended in a British surrender on May 8.
Spain never officially signed an alliance with the American revolutionaries, as King Charles III was hesitant about the precedent he might be setting by encouraging the population of another empire to overthrow their monarch. However, Spain also wanted to regain Gibraltar in the Mediterranean from the British and solidify control of its North American holdings, so it allied itself to France in the international war against Britain. Spain regained West Florida during the fighting and East Florida, which it exchanged for the Bahamas, in the final peace. Though Gibraltar remained in British control, Spain also won all the land surrounding the Gulf of Mexico.