In the history of the United States of America, a slave state was a U.S. state in which the practice of slavery was legal at a particular point in time. A free state was one in which slavery was prohibited. Slavery was an issue that divided the country. It was one of the primary causes of the American Civil War. The Thirteenth Amendment to the United States Constitution, ratified in 1865, abolished slavery in every state and territory of the United States. After that time the terms became more or less obsolete because all states were free of slavery.