In the early stages of the Great Warpresident Woodrow Wilson asked for neutrality and urged the American people not to take sides. The president said that neither side deserved the help of the Americans. This was easier said than done as many current Americans were born in the countries in the war from both sides. The president insisted that the US was neutral but the interests of the country lead toward the allies.
The US traded with both sides of the European conflict, but the ties with the allies were much greater. It pleased the allies greatly to receive the political and business sympathy of the US. One of the first things that Britain did during the war was to cut the transatlantic cable to the US, so all news of the war had to come through Britain. All the news Americans received vilified the Germans so that Americans favoured the allies.
Britain had created a blockade which has effectively started to starve the German people. The new weapon that Germany had created in response to this, the submarine, was wreaking havoc among ships in their submarine zone. Even after these ships sunk ships on which American citizens were travelling, secretary of state William Jennings Bryan still favoured neutrality.
On May 7th, 1915 German submarines attacked the Lusitania, a British passenger ship. Over 1000 passengers died including 128 Americans. Germany knew that the ship secretly carried arms and had warned America ahead of time. In spite of this tragedy president Wilson continued to believe that Americans should not be restricted from travelling the seas. During this time Wilson got re-elected president of the US with a major campaign slogan being "he kept us out of war".
In 1917 a German official named Arthur Zimmerman proposed that Mexico allied itself with Germany and that Germany would give Mexico back all the land the US took from them. This telegram was intercepted by a British official and spread the news to the US. Zimmerman's telegram made Americans eager to humiliate both the Mexicans and the Germans.
Since the US was not truly neutral, the Germans felt they had nothing to lose by an onslaught. They sank one ship after another including the supply ship, the Illinois on March 18th, 1917. In spite of his doubt and anguish, President Woodrow Wilson came before the US congress and asked them to declare war on Germany on April 2nd, 1917