Between 1819 and 1860 events led the United States closer to a civil war. The major issue in these events was slavery in the territories. In 1819 Missouri applied to Congress to join the United States. The admission of Missouri, a slave state, would have upset the balance of 11 slave states and 11 free states that currently existed in the Union. The Missouri Compromise offset the admission of Missouri with that of a free state, Maine. When California sought statehood in 1850 another compromise was needed. The Compromise of 1850 admitted California as a free state, but removed restrictions on slavery in the New Mexico territory and created a stronger fugitive slave law. When conflict arose again over the Kansas and Nebraska territories, Stephen A. Douglas's plan—popular sovereignty—was applied to the new territories. In Kansas, proslavery and antislavery forces clashed violently.
As the issue of slavery divided the nation, a new political party was forged from antislavery Whigs and Democrats and Free-Soilers. The Supreme Court's Dred Scott decision contributed to the controversy. Chief Justice Taney's ruling stated that there was no constitutional provision that could prohibit slavery anywhere. By 1860 many Southerners felt that they could no long stay in the Union. The election of Republican Abraham Lincoln led several Southern states to secede. They formed the Confederate States of America. After Confederate forces fired on Fort Sumter, a federal fort in Charleston Harbor in South Carolina, President Lincoln issued a call for troops. The Civil War had begun.