Most people informed by our modern educational system would respond that the New Deal was ineffective, and that only World War II resolved the Great Depression with its massively non-productive consumption. This is sometimes called "military Keynesianism."
As evidence of this they will point to the renewed slump in US GDP and the equity markets that occurred in 1937.
Here is some perspective on what caused that slump from Paul Kasriel.
In 1937, CPI inflation was running in excess of 4%. So, in 1937, the Fed doubled reserve requirements to soak up excess reserves and prevent even higher inflation. It worked. The economy entered the second leg of the Great Depression in 1937 and deflation re-appeared.
The New Deal was so "ineffective" that the Fed panicked and doubled reserve requirements in a draconian pre-emptive response because they feared inflation! And this was with the unremitting opposition to the reforms of the New Deal by the Republican minority, the Business interests, and their appointees on the Supreme Court.
In a fiat regime inflation and deflation are primarily a policy decision, or perhaps more clearly, the end result of a series of policy, fiscal, and political decisions. Japan is a good example of that combination. There is a lag between the implementation of policy decisions and the desired result. There are also secular events such as a oil embargo or an asset crash that may significantly impact prices and measures of the money supply, although somewhat unevenly.
They are not perfectly controllable, and there is difficulty stimulating aggregate demand and the velocity of money. It cannot be done by monetary policy alone but an accumulation of decisions by the entire national leadership.
But where there is no exogenous constraints such as a monetary standard inflation and deflation are a choice among priorities, essentially a policy decision.
