Why were many Americans committed to isolationism in the 1930s?

Many Americansbelieved that they should not have been involved in WWI was over reaching their boundaries and becoming a global police power. Not only did it violate the Monroe Doctrine of isolationism, but it caused a massive loss of American life, as well as contributed to the economic depression (because soldiers were coming home to no jobs). People started adopting the idea that if its not going on in my back yard than its not significantly important to me.