American politics from the 1840s to the 1860s focused increasingly on two major issues. One was nation-building, specifically the idea of America’s “Manifest Destiny” to control all the territory west to the Pacific and south into Mexico. The other centered around slavery and whether it should be allowed in these new territories that would soon become states.

Rapid Expansion

The first American political parties -- the Federalists and the Republicans -- were gone, replaced by Andrew Jackson’s Democratic Party (formerly the Democratic-Republicans) and the Whigs (formerly the National-Republicans). The election of 1844 was won by Democrat James Polk, at the age of 49 the youngest president elected to date. During his presidency, the United States added a million square miles to its territory. He acquired president-day Oregon, Washington and Idaho from the British, but it took a war to finally gain California and Texas (already annexed and made a state) from the Mexicans. After 16 months of fighting, from April of 1846 to September of 1847, the U.S. established the Rio Grande border and took possession of California.

Divisive Issue of Slavery

Polk, however, had not dealt with the issues of extending slavery into these new territories and Manifest Destiny, which the tumultuous politics of the 1850s swirled around. In 1850, Whig party leader Henry Clay suggested in his “Compromise of 1850” that California be admitted as a free state, but that no mention be made of slavery for Texas and other southwestern states -- effectively making them slave states -- and that the Fugitive Slave Law be enacted in the new states, guaranteeing that civilians would aid in returning escaped slaves.

An Unacceptable Compromise

The Compromise of 1850 pleased neither Northern abolitionists nor the Southern radicals who were already talking about secession. The Kansas-Nebraska Act sponsored by Democratic Sen. Stephen A. Douglas established the principle of “popular sovereignty” in new territories -- i.e., that the white citizens of these soon-to-be states would decide if they wanted slavery or not. Anti-slavery Whigs were so incensed that President Franklin Pierce signed the bill that they left their party and formed the Republican Party as a northern, anti-slavery party.

A Division Lasting Decades

By the 1860 election, both political parties (and the nation) remained polarized around the issue of slavery. The Republicans nominated Abraham Lincoln as their candidate, while the Democrats split into two factions. The moderate Northern Democrats nominated Stephen Douglas, while southern radicals nominated Vice President John C. Breckinridge. Essentially, two races were run, one in the North, which Abraham Lincoln won, and one in the South, won by Breckinridge. Shortly after Lincoln was inaugurated, the Civil War broke out. For decades to come, the Republicans would be the party of the North, while the Democrats would remain the party of the South.