By the end of the war, much of the South's infrastructure had been destroyed. 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 war is one of the most extensively studied and written about episodes in the history of the United States. It remains the subject of cultural and historiographical debate. Of continuing interest is the myth of the Lost Cause of the Confederacy. The war was among the first to use industrial warfare. Railroads, the electrical telegraph, steamships, the ironclad warship, and mass-produced weapons were widely used. The war left an estimated 700,000 soldiers dead, along with an undetermined number of civilian casualties, making it the deadliest in American history. The technology and brutality of the Civil War foreshadowed the coming world wars.