Answer:
U.S. businesses sold war materials to the Allies.
Explanation:
During the first years of WWI, President Woodrow Wilson stated that the US was to remain neutral during the war. However, many US companies were selling food, munitions and raw material to the allies, and indirect way of support. The US also prevented the economic collapse of both France and Britain, with great loans to all the allies countries.
Finally, after the discovery of the Zimmermann Telegram (an offer from Germany inviting Mexico to join the war in return for lands belonging to the US), and several submarine attacks to US-flagged ships, president Wilson asked the congress to declare war, and the US joined WWI on April 6th, 1917.