First, the United States recovered after the crisis in the early 1920s and became one of the most economically developed countries in the world. The United States could afford to donate aid to the countries of Europe affected by the hostilities, including Germany, which was the instigator of World War II.
Second, by helping the countries of Europe to raise their economies, the United States developed its political and economic power. If the countries of Europe remained destroyed, then the external economy of the United States would not develop, no one would buy goods imported into the countries of Europe.
One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.