The Union had many advantages over the Confederacy. The North had a larger population than the South. The Union also had an industrial economy, where- as the Confederacy had an economy based on agriculture. The Union had most of the natural resources, like coal, iron, and gold, and also a well-developed rail system.Slavery played the central role during the American Civil War. The primary catalyst for secession was slavery, especially Southern political leaders' resistance to attempts by Northern antislavery political forces to block the expansion of slavery into the western territories.