Then there was an industrial Recession about 1930. Such things usually last about a year. The government met that crisis by tightening credit and raising import taxes (which precipitated foreign countries raising import taxes against our products).
Then, in 1932 the New Deal was swept into office. It continued to restrict credit, let manufacturing business go bankrupt and kept the Smoot Hawley taxes in force (you should read about them), and, then, worst of all, failed to notice we were facing a FAMINE caused by the worst drought in modern American history.
Most of Oklahoma had blown away before Congress acted and no one knows if FDR ever acknowledged that problem.
By that time the Great Depression was underway and the Democrats did nothing whatsoever to put an end to it.
Phase IV occurred the day Ronald Reagan was elected President. He ended the Great Depression and the New Deal in one fell swoop. Tariffs were dropped. Taxes were dropped. Prosperity returned.