Keynesian
British economist John Maynard Keynes argued in General Theory of Employment Interest and Money that lower aggregate expenditures in the economy contributed to a massive decline in income and to employment that was well below the average. In such a situation, the economy reached equilibrium at low levels of economic activity and high unemployment.
Keynes' basic idea was simple: to keep people fully employed, governments have to run deficits when the economy is slowing, as the private sector would not invest enough to keep production at the normal level and bring the economy out of recession. Keynesian economists called on governments during times of economic crisis to pick up the slack by increasing government spending and/or cutting taxes.
As the Depression wore on, Franklin D. Roosevelt tried public works, farm subsidies, and other devices to restart the US economy, but never completely gave up trying to balance the budget. According to the Keynesians, this improved the economy, but Roosevelt never spent enough to bring the economy out of recession until the start of World War II.
Read more about this topic: Great Depression, Causes, Demand-driven