The US wasn't involved in any physical fighting prior to the attack on Pearl Harbor but we were sending supply convoys to Great Britain.
At the turn of the century, many countries were rich, people believed that social justice was being ensured and that countries were prospering. Others lived in fear because they were aware of the militaristic policies and they noticed that the militaries of all countries increased twice in size. Everything seemed as if things were going well while in reality people were preparing for a mass scale war which resulted with WW1.
There was a quick u.s. victory in both