On September 23, 1810, a group of pro-American men living in Spanish West Florida attacked the Spanish Fort San Carlos in Baton Rouge and established the Republic of West Florida.
Although the Lone Star flag of the short-lived Republic of West Florida probably never flew over Dauphin Island during that republic's 74 day existence, this free and independent republic claimed Dauphin Island along with all the area between the Mississippi and Perdido rivers below the 31st parallel. U.S. President Madison's October 27, 1810 proclamation authorized the United States to ignore West Florida sovereignty and to occupy this territory in the name of the United States.
https://millercenter.org/the-presidency/presidential-speeches/october-27-1810-proclamation-occupation-west-florida
This action further added to the eventual collapse of  Spanish authority on the Gulf. An act of Congress on February 12, 1813, authorized President Madison to use both the U.S. Army and U.S. Navy to expel the Spanish on Mobile Bay and to establish U.S. sovereignty. Despite their April 1813 surrender of Dauphin Island and Mobile Bay, the Spanish did not formally relinquish her claim to Dauphin Island until the 1819 signing of the Adams-Onis Treaty in which the U.S. acquired the present-day state of Florida.