On June 21, 1779, Spain came to the aid of the rebelling American colonists by formally declaring war on Great Britain. The primary role played by Texas in the conflict was to supply Spanish forces mounting an assault on British territory from Louisiana.
King Carlos III commissioned Bernardo de Gálvez to conduct a campaign against the British along the Mississippi River and the Gulf Coast. In order to feed his troops, Gálvez sent an emissary, Francisco García, to Texas governor Domingo Cabello y Robles requesting the delivery of Texas cattle to Spanish forces in Louisiana.
Accordingly, between 1779 and 1782, 10,000 cattle were rounded up on ranches belonging to citizens and missions of Bexar and La Bahía. Rancho de la Mora was typical of these ranches, and escorts were provided from small posts like the Fuerte de Santa Cruz del Cíbolo. From Presidio La Bahía, the assembly point, Texas rancheros and their vaqueros trailed these herds to Nacogdoches, Natchitoches, and Opelousas for distribution to Gálvez's forces.
Fueled in part by Texas beef, Gálvez and his men defeated the British in battles at Manchac, Baton Rouge, Natchez, Mobile, Pensacola, and New Providence in the Bahamas. He was busy preparing for a campaign against Jamaica when peace negotiations ended the war.
From Texas State Historical Association