Answer:
Germany's return to unrestricted submarine warfare
Step-by-step explanation:
When Germany violated their ledge to suspend unrestricted submarine warfare in the North Atlantic and the Mediterranean, the 28th president of the United States of America, Woodrow Wilson, went before the congress to request a declaration of war against the Europe power house. On April 4 1917, the senate arm of the congress passed a vote in support of the proposed war on Germany.
Germany’s resumption of submarine attacks on ships in that year was main reason behind the decision of the united states president to lead the entire country into world war 1.