What was issued by the german government in 1916 to appease the united states and end "unrestricted submarine warfare"? a. the sussex pledge b. the schlieffen plan c. the zimmerman telegram d. the lusitania doctrine?

Correct  a. The Sussex Pledge

Explanation/details:

Public outrage in the US against the Germans swept the nation following the sinking of the British ocean liner, Lusitania, which had happened in May, 1915.  When a German U-boat (submarine) sank the Lusitania, over 1,000 persons were killed, including more than 100 Americans. The passenger liner was targeted by the Germans because they suspected weapons were being shipped to Britain in the cargo hold of the ship.  After the Sussex, a French passenger ferry, was sunk in 1916, the US demanded and got a promise from Germany to stop their unrestricted submarine attacks.  Germany managed to stave off American entry into the war at that time by the Sussex Pledge.  But two years, later, beginning February 1, 1917, the Germans resumed such attacks. This poised America to go to war.