The foreign policies adopted after the WWI were the establishment of treaties in the 1920s and Isolationism in the 1930s.
The first foreign policy that the U.S. adopted consisted of treaties to prevent war, such as the treaties resulting from the Naval Conference (1921–22) that limited the naval arms race and worked out security agreements in the Pacific area between United States, Japan, China, France, Britain, Italy, Belgium, Netherlands, and Portugal. And the Kellogg-Briand pact (1928), in which Germany, France, and the United States agreed to outlaw war in case they incurred in disputes or conflicts.
Nevertheless, these treaties didn’t succeed, therefore in the 1930s, the U.S. acquire the policy of isolationism with regards to the internal affairs of other nations.
The nation decided to stay out of global affairs, avoid political or economic alliances that didn't serve American interests and focused on domestic issues instead.
The Johnson Act (1934) and the Neutrality acts (1935) are examples of the new national policy, in which the U.S. prevented economic and military aid to any country involved in the European disputes that were to escalate into World War II.