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's New Deal is the plan that brought the U.S. out of the Great