Adams–Onís Treaty

The Adams–Onís Treaty (Spanish: Tratado de Adams-Onís) of 1819, also known as the Transcontinental Treaty, the Spanish Cession, the Florida Purchase Treaty, or the Florida Treaty, was a treaty between the United States and Spain in 1819 by which Spain ceded Florida to the United States; in return, the United States renounced its claims to Texas, fixing the boundary along the Sabine River.

Florida had become a burden to Spain, which could not afford to send settlers or staff garrisons, so Madrid decided to cede the territory to the United States in exchange for settling the boundary dispute along the Sabine River in Spanish Texas. The treaty, named for signatories John Quincy Adams and Luis de Onís, established the boundary of U.S. territory and claims through the Rocky Mountains and west to the Pacific Ocean, in exchange for Washington paying residents' claims against the Spanish government up to a total of 5 million Spanish dollars (purchasing power equivalent to US$105,200,000 in 2025) and relinquishing the U.S. claims of Spanish Texas west of the Sabine River and other Spanish areas, under the terms of the Louisiana Purchase.

The treaty remained in full effect for only 183 days: from February 22, 1821, to August 24, 1821, when Spanish military officials signed the Treaty of Córdoba acknowledging the independence of Mexico. The Treaty of Limits between Mexico and the United States, signed in 1828 and effective in 1832, recognized the border defined by the Adams–Onís Treaty as the boundary between the two nations.