The last significant battles raged around the ten-month Siege of Petersburg, gateway to the Confederate capital of Richmond. The Confederates abandoned Richmond, and on April 9, 1865, Lee surrendered to Grant following the Battle of Appomattox Court House, setting in motion the end of the war. A wave of Confederate surrenders followed. On April 14, just five days after Lee's surrender, Lincoln was assassinated. As a practical matter, the war ended with the May 26 surrender of the Department of the Trans-Mississippi but the conclusion of the American Civil War lacks a clear and precise historical end date. Confederate ground forces continued surrendering past the May 26 surrender date until June 23. By the end of the war, much of the South's infrastructure was destroyed, especially its railroads. The Confederacy collapsed, slavery was abolished, and four million enslaved black people were freed. The war-torn nation then entered the Reconstruction era in an attempt to rebuild the country, bring the former Confederate states back into the United States, and grant civil rights to freed slaves. The Civil War is one of the most extensively studied and written about episodes in U.S. history. It remains the subject of cultural and historiographical debate. Of particular interest is the persisting myth of the Lost Cause of the Confederacy. The American Civil War was among the first wars to use industrial warfare. Railroads, the telegraph, steamships, the ironclad warship, and mass-produced weapons were all widely used during the war. In total, the war left between 620,000 and 750,000 soldiers dead, along with an undetermined number of civilian casualties, making the Civil War the deadliest military conflict in American history. The technology and brutality of the Civil War foreshadowed the coming World Wars. Causes of secession The causes behind Southern states' decision to secede were complex and have been historically controversial; most academic scholars identify slavery as the central cause of the war. The causes are further complicated by some historical revisionists who have tried to offer a variety of reasons for the war. Slavery was the central source of escalating political tension in the 1850s. The Republican Party was determined to prevent any spread of slavery to the territories, which, after they were admitted as states, would give the North greater representation in Congress and the Electoral College. Many Southern leaders had threatened secession if the Republican candidate, Lincoln, won the 1860 election. After Lincoln