For four years between 1861 and 1865 the United States engaged in a civil war. Divisions between the free North and the slaveholding South erupted into a full-scale conflict after the presidential election of Abraham Lincoln in 1860. Eleven southern states seceded from the Union, collectively turning their back on the idea of a single American nation. Lincoln, who had been in office for only six weeks, declared these acts of secession illegal, and asked Congress for 500,000 soldiers to crush what threatened to be an aggressive rebellion. In April 1861, the first shots were fired and what followed became a national tragedy of unimaginable proportions. Almost 620,000 soldiers were killed and millions more wounded; large sections of the South were ravaged by violent battles; and the Union nearly collapsed under determined Confederate forces.