The United States decided to enter the war in response to ... France's fall to the Central Powers. Germany's return to unrestricted submarine warfare. the Czar's growing support in Russia. a filibuster by United States senators.

Germany's return to unrestricted submarine warfare

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.

Germany' return to unrestricted submarine warfare

Explanation:

The united states led by president Woodrow Wilson decided to join world war I, because Germany returned to unrestricted submarine warfare in the Northatlantic and Mediterranean sea attacking and sinking both Merchant ships and Military ships. thereby breaking it pledge.

In 1917 the congress voted in favor of the U. S joining the world war I after president Woodrow Wilson had brought the matter for Congress to vote on it. the U. S joined the allied forces of Britain in the fight against Germany during world war I and the Germans were defeated.