A writ of habeas corpus is a legal order enabling an individual to seek release from unlawful detention. The Constitution allows Congress to suspend the writ of habeas corpus for public safety in times of rebellion or invasion. Congress was not in session when Confederate forces initiated the Civil War in April 1861 by attacking U.S. troops stationed at Fort Sumter in South Carolina. Acting quickly against the insurrection, President Abraham Lincoln suspended the writ of habeas corpus. He later asked Congress to approve his controversial action.