Through most of its history, the US had heeded president George Washington's advice in his Farewell Address that the country remain neutral and avoid foreign entanglements. This strategy had worked successfully, allowing the US to quietly emerge as a powerful nation by the end of the 19th century.
In the 1930s, most of the country did not perceive the US as a dominant superpower (the mantle still rested on England, though its star was fast fading) and also didn't see our role as that of the world's policeman. Further, while Europeans by far bore the brunt of the losses in World War I, enough US troops had died in that "foreign" war that Americans were reluctant to get involved there again. People saw and wanted to avoid the clearly unstable overseas situation brought on by Hitler's aggressive policies. The idea of intervention was politically unpopular: many people believed it wasn't our problem to get involved in what was happening across the ocean, even if it did pose an indirect threat to us.
During the 1930s, Congress passed four separate Neutrality Acts in response to events in Europe, which made it more difficult for Roosevelt to prepare for the war he knew was coming.
The United States was hesitant to get involved in world affairs in the 1930s. There are several reasons for this. One factor was we were dealing with our worst depression ever. At the height of the Great Depression, we had 25% of our population unemployed. We had so many economic problems. We really couldn’t worry about world affairs at this time.
We were also concerned about reports that we entered World War I so our businesses could profit. This was the conclusion of the Nye Committee. This angered many people who didn’t want this to happen again. Congress passed several neutrality laws to reduce the likelihood this would occur again.
We were also tired of dealing with world problems. This feeling developed in the 1920s and continued into the 1930s. Getting involved in world affairs carried risk. We could end up being dragged into another conflict so soon after World War I ended. Nobody in our country was ready to possibly go to war again so soon.