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In 1854, Illinois Senator Stephen A. Douglas proposed that two new states, Kansas and Nebraska, be established in the Louisiana Purchase west of Iowa and Missouri. 

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In 1854, Illinois Senator Stephen A. Douglas proposed that two new states, Kansas and Nebraska, be established in the Louisiana Purchase west of Iowa and Missouri. 

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In 1848, the Treaty of Guadelupe Hidalgo ended the Mexican War and added more than 1 million square miles, an area larger than the Louisiana Purchase, to the United States.

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In 1848, the Treaty of Guadelupe Hidalgo ended the Mexican War and added more than 1 million square miles, an area larger than the Louisiana Purchase, to the United States.

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Texas joined the union as a slave state in February 1846; in June, after negotiations with Great Britain, Oregon joined as a free state.

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Texas joined the union as a slave state in February 1846; in June, after negotiations with Great Britain, Oregon joined as a free state.

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cotton planter James K. Polk was elected to the presidency in 1844

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cotton planter James K. Polk was elected to the presidency in 1844

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Slavery Prohibited North of the Southern Boundary. 

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Slavery Prohibited North of the Southern Boundary. 