During the world War I, European countries conducted naval blockade that was intended to prevent their oppositions from receiving supplies and sold their product overseas.
At that time, USA was a neutral country that did not wanted to be involved in the war. But, the blockade still affected the traders from United States.
The blockade by the Britain army caused a lot of Damage to Germany. in retaliation, Germany started to ordered their submarines to shoot the ships that pass across the northern Sea. They intended to shoot British' ships, but a lot of American ships were caught in the crossfire. This caused the people of United States pushed the government to join the allied Forces during the war to fight off Germany.
