Keynesian Theory and the New Deal The crash of the stock market brought many hard times. Franklin D. Roosevelt's New Deal was a way to fix these times. John Stuart Mill and John Maynard Keynes were two economists whose economic theories greatly influenced and helped Franklin D. Roosevelt devise a plan to rescue the United States from the Great Depression it had fallen into. John Stuart Mill was a strong believer of expanded government, which the New Deal provided. John Maynard Keynes believed in supply and demand, which the New Deal used to stabilize the economy. Franklin D. Roosevelt'