The new republic comprised territory south of the 31st parallel, west of the Perdido River to the Mississippi River but north of Lake Pontchartrain. The southern boundary was the Gulf of Mexico.

Americans in the region fervently believed that West Florida rightfully belonged to the United States by the terms of the Louisiana Purchase (1803), a view shared by federal officials in the nation's capital, notably Pres. Thomas Jefferson and his successor, James Madison. Consequently, small groups of locals, some tacitly supported by federal officials, undertook efforts to subvert Spanish sovereignty in the region in the decade after the Purchase. The dispute was especially intense along the colony's western border, in the area known as Feliciana in what is now Louisiana, where as early as 1804 efforts to liberate portions of the province or even annex it to the United States took place.

In 1810, a large organized group of American sympathizers living around Baton Rouge seized the Spanish post there and established the independent "Republic of West Florida." The nascent "republic" sent commissioners to Mobile and Pensacola shortly afterward, hoping to encourage sympathizers in those communities to also rebel and send military forces against local Spanish authorities, or seize control of the entire colony. Little ultimately came of these actions, although malcontents north of Mobile did plan an insurgent expedition of their own. The small force of a few dozen men got as far as camping along the rivers north of the city but made no threat on its military command center of Fort Carlota (originally built by the French in 1723 as Fort Condé). In December of that year, rebels and Spanish authorities clashed north of Mobile on Saw Mill Creek, with reports of the incident indicating that four sympathizers and two Spaniards were killed. Seizing the opportunity presented by the upheaval, Pres. Madison quickly moved to proclaim control of that portion of West Florida in control of the rebels, stretching from the Mississippi River to the Pearl River, adding it to the U.S.-controlled Orleans Territory (the future state of Louisiana). He ordered Orleans territorial governor William C. C. Claiborne to occupy the region with his troops.

In acts passed by Congress in 1811 and 1812, the United States laid unofficial claim to the remainder of West Florida between the Pearl and Perdido Rivers, adding that section of the colony to official jurisdictions related to the Mississippi Territory (the future states of Mississippi and Alabama) and naming Mobile as the administrative center for the region. Territorial governor David Holmes even appointed government officials for the new addition. Spain viewed all of these actions as illegitimate, however, and continued to maintain a garrison in Mobile.

During the War of 1812, U.S. military forces finally moved to occupy the Mobile area by force, ostensibly to prevent the Spanish from using it to supply aid to the British. On April 12, 1813, U.S. general James Wilkinson arrived at the city with a large combined army and navy force and demanded the surrender of Fort Carlota. Severely outnumbered, its commander, Capt. Cayetano Perez, did so without firing a shot the next day. With the departure of Mobile's Spanish garrison, the United States at last formally took possession of the region between the Pearl and Perdido Rivers. The remainder of the original colony of West Florida, lying east of the Apalachicola River, later came under American control through the terms of the Adams-Onis Treaty (1819), which outlined the official cession of the entirety of Florida to the United States.

history of REPUBLIC OF WEST FLORIDA http://archive.tuskegee.edu/gchr/wp-content/uploads/2017/01/gchr-07-02-1992.pdf