California was admitted to the Union as the 31st state, and New Mexico Territory (which included present-day Arizona) and Utah Territory (which included present-day western Colorado and Nevada) were organized, by acts signed by President Millard Fillmore on September 9, 1850. That day, President Fillmore also signed an act paying Texas $10 million to relinquish its claims to the Rio Grande as its western border all the way into Colorado.
California was admitted as a free state — that is, no slavery — upsetting the balance between free and slave states that had held for nearly 30 years. The territorial organic acts for New Mexico and Utah stated: “That, when admitted as a State, the said territory, or any portion of the same, shall be received into the Union, with or without slavery, as their constitution may prescribe at the time of their admission.” This too was an undoing of the Missouri Compromise of 1820-1821, which had prohibited slavery in territories north of 36º 30′ (the southern boundary of Missouri). The question was now open in territories both north (Utah) and south (New Mexico) of that line.
Slavery in the territories became the prime issue of the 1850s, the election of 1860, and the coming of the Civil War.