Answer:
The Sussex Pledge.
Step-by-step explanation:
The Sussex Pledge was a pledge signed by the German government in May 14, 1916 to stop sinking non-military merchant marine and passenger ships.
It also established that German government would provide warning before sinking any merchant or passenger ships for the safety of passengers and crew.
However, this pledge lasted only till 1917 because the German government deemed it as unfeasible and impractical.