The act of entering any kind of war is not an action taken lightly. The U.S. government faced many obstacles at the prospect of entering into WW1. Leonard Woods and Theodore Roosevelt led a campaign to strengthen the U.S. military when the war first began.
In 1915, a movement began and argued that the U.S. needed to build strong naval and land forces thinking the U.S. would eventually be in the war. There was strong opposition to this. It moved quickly through Protestant churches and women's groups. The Democratic party also saw this as a threat. Theodore Roosevelt was a strong candidate for the presidency. The problem was, the U.S. military was, in fact, not ready or in shape to enter war.
In 1917 the Germans sunk one of the U.S. naval ships, and this was the event that pushed us into war. The U.S. had to make the American people understand that war was the right answer. They had to convince businesses that they would succeed and not fail during the war. The war itself, still faced opposition, but for the most part Americans supported our military in their efforts. The entry into the war, was one that was not taken lightly. The U.S. went to great lengths to make sure our military was as prepared as they could be, and the rest of Americans knew the risks and benefits of going to war with Germany, of course this wouldn't be the last war we had with Germany. This war prepared the U.S. for the horrors they were soon to face.