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map of the United States in 1820

This map shows the United States as it existed in 1810, with past and future territorial expansion. Compiled by H. George Stoll, Hammond Incorporated, 1967; revised by U.S. Geological Survey, 1970. From The National Atlas of the United States of America (Washington, D.C.: U.S. Dept. of the Interior, Geological Survey, 1970). About the map

Florida New Spain Louisiana Missouri Territory Arkansaw Territory Missouri Red River Basin Maine

In the early years of the republic, when the Northern states were providing for immediate or gradual emancipation of the slaves, many leaders had supposed that slavery would die out. In 1786 George Washington wrote that he devoutly wished some plan might be adopted “by which slavery may be abolished by slow, sure, and imperceptible degrees.” Virginians Jefferson, Madison, and Monroe and other leading Southern statesmen made similar statements.

The Northwest Ordinance of 1787 had banned slavery in the Northwest Territory. As late as 1808, when the international slave trade was abolished, there were many Southerners who thought that slavery would soon end. The expectation proved false, for during the next generation, the South became solidly united behind the institution of slavery as new economic factors made slavery far more profitable than it had been before 1790.

Chief among these was the rise of a great cotton-growing industry in the South, stimulated by the introduction of new types of cotton and by Eli Whitney’s invention in 1793 of the cotton gin, which separated the seeds from cotton. At the same time, the Industrial Revolution, which made textile manufacturing a large-scale operation, vastly increased the demand for raw cotton. And the opening of new lands in the West after 1812 greatly extended the area available for cotton cultivation. Cotton culture moved rapidly from the Tidewater states on the East Coast through much of the lower South to the delta region of the Mississippi and eventually to Texas.

Sugar cane, another labor-intensive crop, also contributed to slavery’s extension in the South. The rich, hot lands of southeastern Louisiana proved ideal for growing sugar cane profitably. By 1830 the state was supplying the nation with about half its sugar supply. Finally, tobacco growers moved westward, taking slavery with them.

Henry Clay

Henry Clay arranged the Missouri Compromise to maintain the balance between slave and free states. About the illustration

As the free society of the North and the slave society of the South spread westward, it seemed politically expedient to maintain a rough equality among the new states carved out of western territories. In 1818, when Illinois was admitted to the Union, 10 states permitted slavery and 11 states prohibited it; but balance was restored after Alabama was admitted as a slave state. Population was growing faster in the North, which permitted Northern states to have a clear majority in the House of Representatives. However, equality between the North and the South was maintained in the Senate.

In 1819 Missouri, which had 10,000 slaves, applied to enter the Union. Northerners rallied to oppose Missouri’s entry except as a free state, and a storm of protest swept the country. For a time Congress was deadlocked, but Henry Clay arranged the so-called Missouri Compromise: Missouri was admitted as a slave state at the same time Maine came in as a free state. In addition, Congress banned slavery from the territory acquired by the Louisiana Purchase north of Missouri’s southern boundary. At the time, this provision appeared to be a victory for the Southern states because it was thought unlikely that this “Great American Desert” would ever be settled. The controversy was temporarily resolved, but Thomas Jefferson wrote to a friend that “this momentous question, like a fire bell in the night, awakened and filled me with terror. I considered it at once as the knell of the Union.”



In 1819, Spain ceded (gave up) Florida to the United States. What had been “Western Florida” became parts of the new states of Alabama, Mississippi, and Louisiana.

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New Spain

The 1819 treaty between the United States and Spain also set the boundary between the U.S. and New Spain, the Spanish territories in North America. In 1821, Mexico achieved its independence, and the territory shown here in orange became part of the new nation of Mexico.

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The area north and west of New Orleans had been settled by the French and Spanish for centuries, and after the Louisiana Purchase it was quickly organized into the state of Louisiana.

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Missouri Territory

Most of the Louisiana Purchase was organized into the Missouri Territory, named for the Missouri River that ran through it.

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Arkansaw Territory

The region just north of the state of Louisiana was organized into the Arkansaw Territory. It would later become the state of Arkansas and part of Oklahoma.

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The southernmost part of the Missouri Territory had enough white population by 1820 that residents wanted to enter the union as a state. Their desire to become a slave state set off protests and debates that ended in the Missouri Compromise.

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Red River Basin

The Red River Basin was not part of the Lousiana Purchase but was obtained from Great Britain by a treaty in 1818. The treaty declared the boundary between the U.S. and Canada to be the 49th parallel — that is, the line of latitude at 49 degrees north of the equator — as far west as the Rocky Mountains.

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As part of the Missouri Compromise, Maine entered the union as a free state in 1820. The compromise kept the number of slave and free states equal to ensure their equal representation in the Senate.

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