In 1819, the Adams-Onis Treaty was signed, which established the border between Spanish Texas and Louisiana. The border between the two was set along the Sabine River and the 32nd parallel, which placed the Caddo Lake Area within the borders of Texas. In 1821, after 11 years of fighting, the Spanish territory of Mexico won its independence. This included the area of the present-day Caddo Lake state park. Winning the Texas Revolution allowed the Republic of Texas to become independent from Mexico and be annexed by the United States.