The United States took possession in 1803, and in 1804 the territory was divided into two parts. The southern part, which was called the Territory of Orleans, was admitted to the Union in 1812 as the state of Louisiana. Settlement (1819) of theWest Florida Controversy gave Louisiana the area between the Mississippi and Pearl rivers, which formerly had been part of Florida. After statehood French and Spanish influence remained, not only in the Creole and Cajun societies but also in the civil law (based on French and Spanish codes) and in the division of the state into parishes rather than counties. In the early years of the 19th cent. the diverse people of Louisiana—the French, the Spanish, the Germans, and Isleños brought by Gálvez from the Canary Islands—united behind Andrew Jackson to defeat (1815) the British at the Battle of New Orleans during the War of 1812.
With settlers pouring in from other Southern states, great sugar and cotton plantations developed rapidly in the fertile lowlands, and the less productive uplands were also settled. The state capital was moved several times, finally to Baton Rouge in 1849. The advent of steam propulsion on the Mississippi (the first steamboat to navigate the river arrived in New Orleans in 1812) was a boon to the state’s economy; by 1840, New Orleans was the nation’s second largest port. Plantation owners, with their large landholdings and many slaves (more than half the population) dominated politics and largely controlled the state.