Ten Bloodest Battles of the Civil War By Floyd002 Feb 13, 1862 Fort Donelson 19,455 Casualties Period: Feb 13, 1862 to May 8, 1864 Ten Bloodest Battles of the Civil War Apr 6, 1862 Shiloh 23,741 Casualties Aug 29, 1862 Second Bull Run/Manassas 25,251 Casualties Sep 17, 1862 Antietam 26,134 Casualties Dec 31, 1862 Stones River 24,645 Casualties May 1, 1863 Chancellorsville 30,099 Casualties Jul 1, 1863 Gettysburg 51,112 Casualties Sep 19, 1863 Chickamauga 34,624 Casualties May 5, 1864 The Wilderness 25,416 Casualties May 8, 1864 Spotsylvania 27,399 Casualties