President Woodrow Wilson wanted to keep the United States neutral during World War I, but that obviously did not work out. Wars are a lot of money and are very demanding on the civilians, no country truly wants to go to war. He was keeping the United States and the people in his best interest, trying to do what was best for them and the country.
Eventually, this was deemed to be too difficult. Germany was becoming more aggressive and the United States was leaning towards joining the war. A British ship, called the Lusitania, with Americans on board got sunk by Germany, which caused outrage. This did not cause the United States to join the war yet though, although it was a crucial piece of why they did.
The Zimmerman Telegram is known to be the last straw for the United States and the final reason why they joined World War I. The British seized a telegram which was from Germany to Mexico. It stated that if Mexico were to side with Germany during the war and attack the United States, they would get territories within the United States. This caused President Woodrow Wilson to declare war and finally join World War I.
Wilson tried his best to stay neutral during the beginning parts of World War I, he wanted peace and for the world to want it as well. Even though the Lusitania got sunk, he still wanted to try to prevent the United States from joining the war. He did not want the burden of war on his country and on his people.