"Before Spain entered the American Revolutionary War, Gálvez did much to aid the American patriots. He corresponded directly with Patrick Henry, Thomas Jefferson, and Charles Henry Lee, personally received their emissaries, Oliver Pollock and Capt. George Gibson, and responded to their pleas by securing the port of New Orleans so that only American, Spanish, and French ships could move up and down the Mississippi River. Over the river, a veritable lifeline, great amounts of arms, ammunition, military supplies, and money were delivered to the embattled American forces under George Washington and George Rogers Clark. Spain formally declared war against Great Britain on June 21, 1779, and King Carlos III commissioned Gálvez to raise a force of men and 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, with a letter 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. 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. Providing escorts for these herds were soldiers from Presidio San Antonio de Béxar, Presidio La Bahía, and El Fuerte del Cíbolo, and several hundred horses were also sent along for artillery and cavalry purposes. Fueled in part by Texas beef, Gálvez, with 1,400 men, took to the field in the fall of 1779 and defeated the British in battles at Manchac, Baton Rouge, and Natchez.
On March 14, 1780, after a month-long siege with land and sea forces, Gálvez, with over 2,000 men, captured the British stronghold of Fort Charlotte at Mobile. The climax of the Gulf Coast campaign occurred the following year when Gálvez directed a joint land-sea attack on Pensacola, the British capital of West Florida. He commanded more than 7,000 men in the two-month siege of Fort George in Pensacola before its capture on May 10, 1781.
On May 8, 1782, Gálvez and his Spanish forces captured the British naval base at New Providence in the Bahamas. He was busy preparing for a grand campaign against Jamaica when peace negotiations ended the war. After the fighting, Gálvez helped draft the terms of treaty that ended the war, and he was cited by the American Congress for his aid during the conflict." (Wording from http://www.tshaonline.org/handbook/online/articles/fga10)