<P> After the war began in 1914, the United States proclaimed a policy of neutrality despite president Woodrow Wilson's antipathies against Germany . Early in the war, the United States started to favor the British and their allies . President Wilson aimed to broker a peace and sent his top aide, Colonel House, on repeated missions to the two sides, but each remained so confident of victory that they ignored peace proposals . </P> <P> When the German U-boat U-20 sank the British liner Lusitania on 7 May 1915 with 128 US citizens aboard, Wilson demanded an end to German attacks on passenger ships, and warned that the US would not tolerate unrestricted submarine warfare in violation of international law and of human rights . Wilson's Secretary of State, William Jennings Bryan, resigned, believing that the President's protests against the German use of U-boat attacks conflicted with America's official commitment to neutrality . On the other hand, Wilson came under pressure from war hawks led by former president Theodore Roosevelt, who denounced German acts as "piracy", and from British delegations under Cecil Spring Rice and Sir Edward Grey . </P> <P> U.S. Public opinion reacted with outrage to the suspected German sabotage of Black Tom in Jersey City, New Jersey on 30 July 1916, and to the Kingsland explosion on 11 January 1917 in present - day Lyndhurst, New Jersey . </P> <P> Crucially, by the spring of 1917 President Wilson's official commitment to neutrality had finally unraveled . Wilson realized he needed to enter the war in order to shape the peace and implement his vision for a League of Nations at the Paris Peace Conference . </P>

What role did the united states play in the first world war