Union General Ulysses S. Grant accepted the unconditional surrender of Confederate forces at Fort Donelson, Tennessee, opening the Confederate heartland.

Union forces began routing a Confederate army at the Battle of Pea Ridge in Arkansas, securing Missouri for the Union for the rest of the Civil War.

USS Monitor and CSS Virginia fought to a bloody standstill at Hampton Roads, the first battle between ironclad warships and the end of wooden naval supremacy.

President Abraham Lincoln signed the Compensated Emancipation Act, freeing roughly 3,100 enslaved people in the District of Columbia nine months before the Emancipation Proclamation.

Confederate forces quietly evacuate Yorktown, Virginia, ending a month-long siege and opening the road toward Richmond for Union General McClellan.

Mexican forces under General Ignacio Zaragoza defeated a larger, better-equipped French army at Puebla, a victory now celebrated as Cinco de Mayo.

News of Mexico's stunning victory over French forces at Puebla spread through Mexico City, cementing General Zaragoza's triumph as a symbol of national resistance.

President Lincoln signed the Morrill Anti-Bigamy Act into law, targeting Mormon polygamy in Utah Territory and igniting decades of federal-religious conflict.

Union and Confederate armies clashed near Sharpsburg, Maryland, in the single bloodiest day of combat in American history, with roughly 22,700 casualties.

Union and Confederate forces clash at the Battle of Shepherdstown, the final engagement of the Maryland Campaign following Antietam.

War-weary Northern voters dealt Republicans losses in the 1862 midterm elections, a rebuke of Lincoln's handling of the Civil War.