At the start of the Civil War (1861–65), President Lincoln aimed to preserve the Union. But this would require the “defeat of the world's most powerful slaveholding class” and abolition of slavery.

Blacks backed the Union and called for slaves’ liberation. In the summer of 1861 bondmen began fleeing to the army at Fortress Monroe, Virginia. Labeled “contrabands” of war, their rising numbers fueled debate on whether to retain and liberate them. Abolitionist Frederick Douglass argued: “A blow struck for the freedom of the slave is equally a blow for the safety and welfare of the country” (Foner, 2000, p. 477). Lincoln hesitated, but early Confederate victories, Union manpower shortages, and his fear that England and France might recognize the Confederacy prodded his Emancipation Proclamation (1863), which freed slaves in Union-controlled areas, exempted border slave states, and approved black military enlistment. Together with the Conscription Act (1863), it shifted the war's goal and stirred racial conflict. New York City, for example, had riots in July. White mobs burned draft offices, federal buildings, and black communities; 105 blacks perished before Union troops restored order.

Still, America embraced Lincoln's “new birth of freedom.” When the war ended half of all eligible northerners had served, compared to three-fourths of southerners. The US Colored Troops and Navy had enlisted nearly 200, 000 blacks. The Union had incurred an estimated 360,000 fatalities; the Confederacy, 258,000. More than 4 million slaves were “forever free” as the Thirteenth Amendment abolished slavery.