Southern anxiety grew as settlers poured into northern territories that were sure to join the Union as free states, thereby tipping the sectional balance of power against the South in Congress and the Electoral College.
The Civil War had a greater impact on American society and the polity than any other event in the country’s history.
It was also the most traumatic experience endured by any generation of Americans.
(Both territories did legalize slavery, but few slaves were taken there.) At the same time, Congress abolished the slave trade in the District of Columbia, ending the shameful practice of buying and selling human beings in the shadow of the Capitol.
But the Compromise of 1850 compensated the South with a tough new fugitive slave law that empowered Federal marshals, backed by the Army if necessary, to recover slaves who had escaped into free states.
But they intended to prevent its further expansion as the first step toward bringing it eventually to an end.
The United States, said Lincoln at the beginning of his famous campaign against Douglas in 1858 for election to the Senate, was a house divided between slavery and freedom.Private armies of "filibusters," composed mainly of southerners, even tried to invade Cuba and Nicaragua to overthrow their governments and bring these regions into the United States as slave states.The events that did most to divide North and South were the Kansas-Nebraska Act of 1854 and the subsequent guerrilla war between pro- and anti-slavery partisans in Kansas territory.The storm was so powerful that it swept away many northern Democrats and gave rise to the Republican party, which pledged to keep slavery out of Kansas and all other territories.An eloquent leader of this new party was an Illinois lawyer named Abraham Lincoln, who believed that "there can be no moral right in the enslaving of one man by another." Lincoln and other Republicans recognized that the United States Constitution protected slavery in the states where it already existed.In the House of Representatives, northern congressmen pushed through the Wilmot Proviso specifying that slavery should be excluded in all territories won from Mexico.In the Senate, southern strength defeated this proviso. Calhoun introduced instead a series of resolutions affirming that slaveholders had the constitutional right to take their slave property into any United States territory they wished.But two years later, running against a Democratic party split into northern and southern factions, Lincoln won the presidency by carrying every northern state.It was the first time in more than a generation that the South had lost effective control of the national government. A growing majority of the American population lived in free states.At least 620,000 soldiers lost their lives in the war, 2 percent of the American population in 1861.If the same percentage of Americans were to be killed in a war fought today, the number of American war dead would exceed 6 million.