Louisiana Was Never Mexican—It Was French, Then American

France claimed La Louisiane (1682), ceded west of Mississippi to Spain (1762), regained it secretly (1800), sold the whole territory to the U.S. (1803)—the Louisiana Purchase. Mexico (independent 1821) never held it. The Sabine River became the U.S.–Mexico border (Adams–Onís Treaty, 1819).

Confusion stems from "Spanish Louisiana" (1762–1800) and later Mexican claims to Texas—but Louisiana proper? Always French → Spanish → French → American.