1) After WWI, the US became increasingly isolationist as the public did not want to be involved in overseas conflicts and feared the costs of future wars.
2) The US rejected the Treaty of Versailles and did not join the League of Nations, reducing its role in global affairs.
3) Through policies like the Fordney-McCumber Tariff and immigration quotas, the US also isolated itself economically and politically in the 1920s in an effort to focus inwardly.