The Trent Affair was a diplomatic crisis between the United States and the United Kingdom which occurred on 8 November 1861 during the American Civil War. A US Navy warship stopped a British steamer at gunpoint in international waters and arrested the Confederate diplomats James Murray Mason and John Slidell, violating international law. British Prime Minister Lord Palmerston was outraged and demanded their immediate release and dispatched 11,000 British Army troops to Canada; hoping to avert war, President Abraham Lincoln quietly released the two diplomats, unwilling to fight another war.