What incident involving a German submarine resulted in the deaths of 139 Americans and pressured the U.S. to take action against Germany?

The incident that involved a German submarine leading to the deaths of 139 Americans and pressuring the United States to take action against Germany is the sinking of the Lusitania. The RMS Lusitania was a British ocean liner that was torpedoed by a German U-boat off the coast of Ireland on May 7, 1915. Although it was not an American ship, it was carrying many American passengers at the time.

The attack on the Lusitania provoked outrage in the United States because it was seen as an unprovoked act of aggression against a civilian vessel. The loss of American lives and the nature of the sinking ignited anti-German sentiment and played a critical role in shifting public opinion in favor of entering World War I. It prompted further discussions regarding U.S. neutrality and the need to protect American citizens on the high seas. This incident ultimately contributed to the deeply intertwined political and social pressures that led the United States to join the war in 1917.