The refusal to join the League of Nations, the raise of the tariffs to imported goods by the Fordney-Mc Number Act and the Emergency Quota Act all point to an increasing isolationist policy from the US (mainly the Congress) in the early 20's.
The League of Nations was a precursor to what nowadays is the UN. It was created after WWI as a way to prevent new wars through a mechanism of collective security. However, its efficacy was severely damaged when the US decided not to join it.
The Fordney-Mc Number Act enforced an increase on the tariffs applied to imported goods from other countries. The objective of the Act was to protect domestic industries and it demonstrated that the US was unwilling to open its market and to enter in stronger trade relations with Europe.
The Emergency Quota Act established a limit in the number of immigrants that could arrive at the US. It mainly affected further immigration from European countries which was soaring because of the economic crisis post WWI.