I've set up a couple of Google Alerts as part of writing my book on the American Revolution. Via this, I was informed that there is an art exhibit in Washington, DC, on the theme of Spanish support for the American Revolution. This is one of those episodes of a Latin American military history that needs to be made more prominent.
Spain's participation in the war focused on retrieving the Gulf Coast, which had fallen into British hands after the end of the Seven Years' War. The British divided the colony into two, and established the capital of West Florida, which included the Florida panhandle and stretched west along the cost to the Mississippi river, at Pensacola.
The Spanish governor of Louisiana (which had been transferred by France to Spain in 1762, although no-one knew until 1764), Bernardo de Gálvez y Gallado, pursued an aggressive campaign against British West Florida following the Spanish declaration of war against Britain in 1779. A summary article outlining Gálvez' actions is found at the Patriot Resource.
The most significant action occurred in 1781, with the siege and battle of Pensacola. This has apparently been described as one of the most written-about battles in history, and extensive excerpts from Gálvez' own combat diary are included at the Florida Historical Quarterly. The Spanish won; and the peace agreements of 1783 that ended the war gave them back both of the Floridas. Of course, the actual northern boundary of the Floridas was not carefully delineated in all the agreements, and the resultant dispute returned relations between Catholic Spain and Protestant Anglo-America back to their frigid normal state.
If you haven't got time to read so much as I offer in my links, you could do worse than read the summary of events at Little Town Mart.