Which economic belief did John Maynard Keynes advocate in the first half of the 20th century?

John Maynard Keynes advocated the belief that large government spending can stimulate an economy during periods of decline. This concept arose from his observations during the Great Depression, where he argued that during economic downturns, private sector demand often falters. Keynes proposed that government intervention, particularly through increased public spending, could help boost aggregate demand, leading to job creation and ultimately economic recovery. He believed that such fiscal measures were essential to counteract the adverse effects of downturns, making them a cornerstone of Keynesian economics. This approach shifted the view of economic policy towards a more active governmental role in managing economic cycles, particularly advocating for increased public expenditure during recessions to spur growth and reduce unemployment.