Question: What was the cause of the Great Depression from the viewpoint of Monetarists?
About the article "Great Depression", section "Monetarist".

Candidate passages:
Heterodox theories.
Austrian School.
Another explanation comes from the Austrian School of economics.
Theorists of the "Austrian School" who wrote about the Depression include Austrian economist Friedrich Hayek and American economist Murray Rothbard, who wrote "America's Great Depression" (1963).
In their view and like the monetarists, the Federal Reserve, which was created in 1913, shoulders much of the blame; but in opposition to the monetarists, they argue that the key cause of the Depression was the expansion of the money supply in the 1920s that led to an unsustainable credit-driven boom.
In the Austrian view it was this inflation of the money supply that led to an unsustainable boom in both asset prices (stocks and bonds) and capital goods.
By the time the Fed belatedly tightened in 1928, it was far too late and, in the Austrian view, a significant economic contraction was inevitable.
In February 1929 Hayek published a paper predicting the Federal Reserve's actions would lead to a crisis starting in the stock and credit markets.
According to the Austrians, the artificial interference in the economy was a disaster prior to the Depression, and government efforts to prop up the economy after the crash of 1929 only made things worse.
According to Rothbard, government intervention delayed the market's adjustment and made the road to complete recovery more difficult.
However, Hayek, unlike Rothbard, also believed, along with the monetarists, that the Federal Reserve further contributed to the problems of the Depression by permitting the money supply to shrink during the earliest years of the Depression. 
In recent years more influential among economists has been the monetarist interpretation of Milton Friedman, which did include a full-scale monetary history of what he calls the "Great Contraction".
Friedman concentrated on the failures before 1933.
He pointed out that between 1929 and 1932, the Federal Reserve allowed the money supply to fall by a third which is seen as the major cause that turned a normal recession into a Great Depression.
Friedman specially criticized the decisions of Hoover and the Fed not to save banks going bankrupt.
Monetarists state that the banking and monetary reforms were a necessary and sufficient response to the crises.
They reject the approach of Keynesian deficit spending. 
There are also various heterodox theories that downplay or reject the views of the Keynesians and monetarists. 
There were multiple causes for the first downturn in 1929.
These include the structural weaknesses and specific events that turned it into a major depression and the manner in which the downturn spread from country to country.
In relation to the 1929 downturn, historians emphasize structural factors like major bank failures and the stock market crash.
In contrast, monetarist economists (such as Barry Eichengreen, Milton Friedman and Peter Temin) point to monetary factors such as actions by the US Federal Reserve that contracted the money supply, as well as Britain's decision to return to the gold standard at pre–World War I parities (US$4.86:£1).
Recessions and business cycles are thought to be a normal part of living in a world of inexact balances between supply and demand.
What turns a normal recession or 'ordinary' business cycle into a depression is a subject of much debate and concern.
Scholars have not agreed on the exact causes and their relative importance.
The search for causes is closely connected to the issue of avoiding future depressions.
A related question is whether the Great Depression was primarily a failure on the part of free markets or a failure of government efforts to regulate interest rates, curtail widespread bank failures, and control the money supply.
Current theories may be broadly classified into two main points of view and several heterodox points of view.
There are demand-driven theories, most importantly Keynesian economics, but also including those who point to the breakdown of international trade, and Institutional economists who point to underconsumption and over-investment (causing an economic bubble), malfeasance by bankers and industrialists, or incompetence by government officials.
The consensus among demand-driven theories is that a large-scale loss of confidence led to a sudden reduction in consumption and investment spending.
Once panic and deflation set in, many people believed they could avoid further losses by keeping clear of the markets.
Holding money became profitable as prices dropped lower and a given amount of money bought ever more goods, exacerbating the drop in demand.
There are the monetarists, who believe that the Great Depression started as an ordinary recession, but that significant policy mistakes by monetary authorities (especially the Federal Reserve), caused a shrinking of the money supply which greatly exacerbated the economic situation, causing a recession to descend into the Great Depression.
Related to this explanation are those who point to debt deflation causing those who borrow to owe ever more in real terms.
There are also various heterodox theories that downplay or reject the explanations of the Keynesians and monetarists.
For example, some new classical macroeconomists have argued that various labor market policies imposed at the start caused the length and severity of the Great Depression.
The Austrian school of economics focuses on the macroeconomic effects of money supply, and how central banking decisions can lead to over-investment (economic bubble). 
There was debate between Monetarists and Keynesians in the 1960s over the role of government in stabilizing the economy.
Both Monetarists and Keynesians are in agreement over the fact that issues such as business cycles, unemployment, inflation are caused by inadequate demand, and need to be addressed, but they had fundamentally different perspectives on the capacity of the economy to find its own equilibrium and as a consequence the degree of government intervention that is required to create equilibrium.
Keynesians emphasized the use of discretionary fiscal policy and monetary policy, while monetarists argued the primacy of monetary policy, and that it should be rules-based.
The debate was largely resolved in the 1980s.
Since then, economists have largely agreed that central banks should bear the primary responsibility for stabilizing the economy, and that monetary policy should largely follow the Taylor rule – which many economists credit with the Great Moderation.
The Global Financial Crisis, however, has convinced many economists and governments of the need for fiscal interventions and highlighted the difficulty in stimulating economies through monetary policy alone during a liquidity trap.