Edwin McMasters Stanton was an American lawyer and politician who served as U.S. Secretary of War under the Lincoln Administration during most of the American Civil War. Stanton's management helped organize the massive military resources of the North and guide the Union to victory. However, he was criticized by many Union generals, who perceived him as overcautious and micromanagerial. He also organized the manhunt for Abraham Lincoln's assassin, John Wilkes Booth.

The secretary of war was a member of the U.S. president's Cabinet, beginning with George Washington's administration. A similar position, called either "Secretary at War" or "Secretary of War", had been appointed to serve the Congress of the Confederation under the Articles of Confederation between 1781 and 1789. Benjamin Lincoln and later Henry Knox held the position. When Washington was inaugurated as the first President under the Constitution, he appointed Knox to continue serving as Secretary of War.