Modern Economic Theories Two controversial economic policies are Keynesian economics and Supply Side economics. They represent opposite sides of the economic policy spectrum and were introduced at opposite ends of the 20th century, yet still are the most famous for their effects on the economy of the United States when they were used. The founder of Keynesian economic theory was John Maynard Keynes. He made many great accomplishments during his time and probably his greatest was what he did for America in its hour of need. During the 1920's, the U.S. experienced a stock market crash of enormous prop