A few good primary sources...

In an effort to preserve the balance of power in Congress between slave and free states, the Missouri Compromise was passed in 1820 admitting Missouri as a slave state and Maine as a free state. Furthermore, with the exception of Missouri, this law prohibited slavery in the Louisiana Territory north of the 36° 30´ latitude line. In 1854, the Missouri Compromise was repealed by the Kansas-Nebraska Act. Three years later the Missouri Compromise was declared unconstitutional by the Supreme Court in the Dred Scott decision, which ruled that Congress did not have the authority to prohibit slavery in the territories.

http://www.loc.gov/rr/program/bib/ourdocs/Missouri.html

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The Treaty of Guadalupe Hidalgo was signed by the United States and Mexico on February 2, 1848, ending the Mexican War and extending the boundaries of the United States by over 525,000 square miles. In addition to establishing the Rio Grande as the border between the two countries, the territory acquired by the U.S. included what will become the states of Texas, California, Nevada, Utah, most of New Mexico and Arizona, and parts of Colorado and Wyoming. In exchange Mexico received fifteen million dollars in compensation for the territory and the U.S. agreed to assume claims from private citizens of these areas against the Mexican government.

http://www.loc.gov/rr/program/bib/ourdocs/Guadalupe.html

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The Compromise of 1850 consists of five laws passed in September of 1850 that dealt with the issue of slavery. In 1849 California requested permission to enter the Union as a free state, potentially upsetting the balance between the free and slave states in the U.S. Senate. Senator Henry Clay introduced a series of resolutions on January 29, 1850, in an attempt to seek a compromise and avert a crisis between North and South. As part of the Compromise of 1850, the Fugitive Slave Act was amended and the slave trade in Washington, D.C., was abolished. Furthermore, California entered the Union as a free state and a territorial government was created in Utah. Also, an act was passed settling a boundary dispute between Texas and New Mexico that also established a territorial government in New Mexico.

http://www.loc.gov/rr/program/bib/ourdocs/Compromise1850.html

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The Kansas-Nebraska Act repealed the Missouri Compromise, allowing slavery in the territory north of the 36° 30´ latitude. Introduced by Senator Stephen Douglas of Illinois, the Kansas-Nebraska Act stipulated that the issue of slavery would be decided by the residents of each territory, a concept known as popular sovereignty. After the bill passed on May 30, 1854, violence erupted in Kansas between pro-slavery and anti-slavery settlers, a prelude to the Civil War.

http://www.loc.gov/rr/program/bib/ourdocs/kansas.html

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The Supreme Court decision Dred Scott v. Sandford was issued on March 6, 1857. Delivered by Chief Justice Roger Taney, this opinion declared that slaves were not citizens of the United States and could not sue in Federal courts. In addition, this decision declared that the Missouri Compromise was unconstitutional and that Congress did not have the authority to prohibit slavery in the territories. The Dred Scott decision was overturned by the 13th and 14th Amendments to the Constitution.

http://www.blogger.com/post-create.g?blogID=5629040858974646181