Summary: U.S. foreign policy differed in the periods following World Wars I and II. Following the conclusions of both wars, an association of nations was proposed in the name of establishing long-lasting peace that would support political independence and territorial integrity for all nations. The United States rejected such an association following World War I, voting against the Treaty of Versailles and the League of Nations and instead opting to continue on an isolationist path. In contrast, the U.S. chose a much more interventionist approach following World War II by supporting and hosting the United Nations, participating in NATO, and fighting against the postwar spread of communism.
Coming out of World War I, the United States emerged as the most powerful nation in the world. The president at this time was the Progressive Woodrow Wilson. Wilson came up with a plan for long lasting peace at the conclusion of the war called the Fourteen Points. One of these points was the League of Nations which was Wilson's favorite thing, very similar to the way Alexander Hamilton felt about the BUS with his financial plan. This part of Wilson's plan stated, "A general association of nations must be formed under specific covenants for the purpose of affording mutual guarantees of political independence and territorial integrity to great and small states alike." However, the United States never signed the Treaty of Versailles and never became a member of the League of Nations. Opposition against Wilson's plans came from within the country. Massachusetts Senator and chairman of the Senate Foreign Relations Committee Henry Cabot Lodge led the fight against signing the Treaty of Versailles and the League of Nations. The American general public shared this sentiment and the country's foreign policy was independent and isolationistic for the next two decades.
Without committing to any lasting foreign relationships, the United States did involve itself with other countries in three regards: war reparations, disarmament and international finance. The Treaty of Versailles hit Germany hard and they had to pay out huge sums of money as reparations. In 1924 American banker Charles Dawes negotiated an agreement with Germany, France, England and the United States which would be known as the Dawes Plan. With this plan, American banks would give enormous loans to Germany so they could pay their reparations and in return England and France would reduce the amount Germany owed. The English and French would then be able to pay debts owed to the United States. The Washington Conference was an attempt to prevent harmful arms races among other things. The Five-Power Pact came from this and it set limits for total naval tonnage as well as a ratio of armaments for the signing countries. Also from the Washington Conference came the Nine-Power Pact which pledged a continuation of the Open Door Policy in China and the Four-Power Pact in which the US, Britain, France and Japan agreed to respect each others Pacific claims and to cooperate to prevent aggression. The Kellogg-Briand Pact finished what the Washington Conference started and several countries signed the treaty outlawing war as an instrument of national policy. At the time Congress was predominately Republican and the Fordney-McCumber Tariff was passed. This tariff was very high and made it tremendously hard for foreign countries to export goods to the United States.