The United States suffered a terrible trial by fire between 1861 and 1865, when civil war broke out between the Northern states and the 11 Southern states that seceded from the country. The war arose from economic and political issues that centered on whether slavery would remain legal. The South left the Union after anti-slavery candidate Abraham Lincoln was elected president in 1860. Lincoln regarded the South’s secession as unlawful, and in April 1861 he ordered troops to recapture a federal fort taken by Southern forces. The war that ensued was bloody, with 1.5 million casualties, including more than 600,000 deaths—almost as many as all other US wars combined.

America was born in compromise. For thousands of years, slavery was considered one of the standard spoils of war, and nations everywhere practiced it. However, the slavery that developed in tandem with European imperialism was unique in both its importance to colonial economies and its reliance on racist ideologies to justify itself. By the late 1700s and early 1800s, a growing middle class in Europe, encouraged by anti-slavery thought leaders, had begun to protest that slavery was barbaric and wrong, and that it had no place in civil society.