Political Causes- Individual states' rights were an issue for the states. Southern states wanted to be able to decide laws without the federal government politically invading their legislature.
Economic Causes- Northern states had economies based in industry, while Southern states depended on slavery to run the agriculture that supported them. If slavery was made illegal at the federal level, this would threaten the southern economy.
Social Causes- Many people in the North felt morally superior to people in the South because Northerners believed that slavery was wrong, while Southerners did not consider slaves to be people.