Isolationism is the policy of not getting involved in foreign affairs. When World war 1 was over the US was not in a place for war. The US had their hands full with domestic affairs, the general aptitude or belief was to stay out of foreign affairs. Because demand was high and supplies where low prices where double. Many Americans supported isolation, but it was impossible to "steer clear of foreign entanglement". The rest of the world owed the US some 13 billion dollars from loans made during WW1, so the US couldn't afford to follow a strict policy of isolationism. As result, in 1921 Calvin Coolidge and Warren Harding signed peace treaties with Germany, Hungary, and Austria.
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