American Civil War: The Battle of Chancellorsville between Robert E. Lee's Confederate Army of Northern Virginia and the Union Army of the Potomac under Joseph Hooker begins.

The American Civil War was a civil war in the United States between the Union and the Confederacy, which was formed in 1861 by states that had seceded from the Union to preserve slavery in the United States, which they saw as threatened because of the election of Abraham Lincoln and the growing abolitionist movement in the North. The war lasted a little over four years, ending with Union victory, the dissolution of the Confederacy and the abolition of slavery, freeing four million African Americans.