Civil War and Reconstruction By msmeyernp Apr 12, 1861 Fort Sumter The first battle of the Civil War Sep 17, 1862 The Battle of Antietam The deadliest single day in US military history. Jul 1, 1863 The Battle of Gettysburg The Battle of Gettysburg lasted for three days, and was the deadliest battle of the Civil War. It was also known as the turning point of the war.