One of the policy prescriptions of the GT for curing recessions was to lower interest rates; another, more potent tool, was to deliberately run a fiscal deficit as a strategy for increasing aggregate demand. The GT was too late to have much of an impact on the Great Depression, but it did have a major impact on the economic policies of the Western Democracies from 1946 to the present.
During the period 1979 to 2001, Keynesianism was supposedly discredited, but national governments continued to use stimulus packages and monetary policy to resolve recessions. The policy has evolved, but remains the cornerstone of actually existing government behavior.
Attacks on Keynesianism: the most famous adversary of the GT was Friedrich von Hayek (1899-1992) of the London School of Economics, who insisted that an authentically free market would be self-correcting if it were only allowed to. Hayek's objections were ideological, but other economists such as John Muth argued that the GT expected people to make irrational, or unreasonable errors.
During the late 1970's, Keynesianism was eclipsed by the Rational Expectations Hypothesis; but REH failed to develop satisfactory policy proposals, while Neo-Keynesian economics evolved to address many of the original REH criticisms.
Sane Person: But doesn't that substitute the political process for the market process in determining how society's scarce resources are allocated? If central economic planning lead to prosperity wouldn't North Korea be the most prosperous place on Earth?
Keynesian: Paul Krugman didn't tell me that, so it can't be true! Racist!