What was unrestricted submarine warfare and why did America enter th war in 1917?
Unrestricted submarine warfare in WWI was the torpedoing of any ships that were travelling to an enemy controlled port that submarines came across even if they were registered in a neutral country (in the case of ww1 the torpedoing of neutral american merchant ships that went to british ports). This severely damaged german public opinion in America. America only joined WWI in 1917 because of the zimmerman telegraph, a top secret german request for Mexico to invade the USA in order to divert American supplies travelling to Britain. This would then give the Germans a better chance against the British. Unfortuantely the British Intelligence services intercepted the telegram and reported it to the Americans who instantly declared war on Germany.
