Question: What, according to the economists, caused the Great Depression in the 1920's?
About the article "Great Depression", section "Inequality".

Candidate passages:
  Ben S. Bernanke.
"Essays on the Great Depression" (2000)  Bernstein, Michael A.
"The Great Depression: Delayed Recovery and Economic Change in America, 1929–1939" (1989) focus on low-growth and high-growth industries  Bordo, Michael D., Claudia Goldin, and Eugene N. White, eds.
"The Defining Moment: The Great Depression and the American Economy in the Twentieth Century" (1998).
Advanced economic history.
Chandler, Lester.
"America's Greatest Depression" (1970).
economic history overview.
De Long, Bradford.
"Liquidation Cycles and the Great Depression" (1991)  Jensen, Richard J.
"The Causes and Cures of Unemployment in the Great Depression," "Journal of Interdisciplinary History" 19 (1989) 553–83.
online at JSTOR in most academic libraries  McElvaine, Robert S. "The Great Depression" (2nd ed 1993) social history  Mitchell, Broadus.
"Depression Decade: From New Era through New Deal, 1929–1941" (1964), standard economic history overview.
Parker, Randall E. "Reflections on the Great Depression" (2002) interviews with 11 leading economists  Salsman, Richard M. “The Cause and Consequences of the Great Depression” in "The Intellectual Activist", ISSN 0730-2355.
Mr. Salsman argues that the Great Depression was "fundamentally" caused by "statist" government policy.
Singleton, Jeff.
"The American Dole: Unemployment Relief and the Welfare State in the Great Depression" (2000)  Warren, Harris Gaylord.
"Herbert Hoover and the Great Depression" (1959).  
Leave-it-alone liquidationism (1929–1933).
From the point of view of today's mainstream schools of economic thought, government should strive to keep some broad nominal aggregate on a stable growth path (for proponents of new classical macroeconomics and monetarism, the measure is the nominal money supply; for Keynesian economists it is the nominal aggregate demand itself).
During a depression the central bank should pour liquidity into the banking system and the government should cut taxes and accelerate spending in order to keep the nominal money stock and total nominal demand from collapsing.
The United States government and the Federal Reserve did not do that during the 1929‑32 slide into the Great Depression The existence of "liquidationism" played a key part in motivating public policy decisions not to fight the gathering Great Depression.
An increasingly common view among economic historians is that the adherence of some Federal Reserve policymakers to the liquidationist thesis led to disastrous consequences.
Regarding the policies of President Hoover, economists like Barry Eichengreen and J. Bradford DeLong point out that the Hoover administration’s fiscal policy was guided by liquidationist economists and policy makers, as Hoover tried to keep the federal budget balanced until 1932, when Hoover lost confidence in his Secretary of the Treasury Andrew Mellon and replaced him.
Hoover wrote in his memoirs he did not side with the liquidationists, but took the side of those in his cabinet with "economic responsibility", his Secretary of Commerce Robert P. Lamont and Secretary of Agriculture Arthur M. Hyde, who advised the President to "use the powers of government to cushion the situation".
But at the same time he kept Andrew Mellon as Secretary of the Treasury until February 1932.
It was during 1932 that Hoover began to support more aggressive measures to combat the Depression.
In his memoirs, President Hoover wrote bitterly about members of his Cabinet who had advised inaction during the downslide into the Great Depression:Before the "Keynesian Revolution", such a liquidationist theory was a common position for economists to take and was held and advanced by economists like Friedrich Hayek, Lionel Robbins Joseph Schumpeter, Seymour Harris and others.
According to the liquidationists a depression is good medicine.
The function of a depression is to liquidate failed investments and businesses that have been made obsolete by technological development in order to release factors of production (capital and labor) from unproductive uses.
These can then be redeployed in other sectors of the technologically dynamic economy.
They pointed to the short duration of the Depression of 1920–21 was due to the policy of letting the liquidation occur and argued that the crisis had laid the groundwork for the prosperity of the later 1920s.
They pushed for deflationary policies (which were already executed in 1921) which – in their opinion – would assist the release of capital and labor from unproductive activities to lay the groundwork for a new economic boom.
The liquidationists argued that even if self-adjustment of the economy took mass bankruptcies, then so be it.
Postponing the liquidation process would only magnify the social costs.
Schumpeter wrote that itDespite liquidationist expectations, a large proportion of the capital stock was not redeployed and vanished during the first years of the Great Depression.
According to a study by Olivier Blanchard and Lawrence Summers, the recession caused a drop of net capital accumulation to pre-1924 levels by 1933. 
In their 1963 book "A Monetary History of the United States, 1867–1960", Milton Friedman and Anna Schwartz laid out their case for a different explanation of the Great Depression.
Essentially, the Great Depression, in their view, was caused by the fall of the money supply.
Friedman and Schwartz write: "From the cyclical peak in August 1929 to a cyclical trough in March 1933, the stock of money fell by over a third."
The result was what Friedman calls the "Great Contraction" — a period of falling income, prices, and employment caused by the choking effects of a restricted money supply.
Friedman and Schwartz argue that people wanted to hold more money than the Federal Reserve was supplying.
As a result people hoarded money by consuming less.
This caused a contraction in employment and production since prices were not flexible enough to immediately fall.
The Fed's failure was in not realizing what was happening and not taking corrective action.
After the Depression, the primary explanations of it tended to ignore the importance of the money supply.
However, in the monetarist view, the Depression was “in fact a tragic testimonial to the importance of monetary forces.” In their view, the failure of the Federal Reserve to deal with the Depression was not a sign that monetary policy was impotent, but that the Federal Reserve implemented the wrong policies.
They did not claim the Fed "caused" the depression, only that it failed to use policies that might have stopped a recession from turning into a depression.
During the post-Civil War period and continuing into the early 20th century, the US and Europe had generally adopted a government-mandated gold standard.
The U.S. economy during this period went through a number of cycles of boom and bust.
The depressions often seemed to be set off by bank panics, the most significant occurring in 1873, 1893, 1901, 1907, and 1920.
Before the 1913 establishment of the Federal Reserve, the banking system had dealt with these crises in the U.S. (such as in the Panic of 1907) by suspending the convertibility of deposits into currency.
Starting in 1893, there were growing efforts by financial institutions and business men to intervene during these crises, providing liquidity to banks that were suffering runs.
During the banking panic of 1907, an ad-hoc coalition assembled by J. P. Morgan successfully intervened in this way, thereby cutting off the panic, which was likely the reason why the depression that would normally have followed a banking panic did not happen this time.
A call by some for a government version of this solution resulted in the establishment of the Federal Reserve.
But in 1928–32, the Federal Reserve did not act to provide liquidity to banks suffering runs.
In fact, its policy contributed to the banking crisis by permitting a sudden contraction of the money supply.
During the Roaring Twenties, the central bank had set as its primary goal "price stability", in part because the governor of the New York Federal Reserve, Benjamin Strong, was a disciple of Irving Fisher, a tremendously popular economist who popularized stable prices as a monetary goal.
It had kept the number of dollars at such an amount that prices of goods in society appeared stable.
In 1928, Strong died, and with his death this policy ended, to be replaced with a real bills doctrine requiring that all currency or securities have material goods backing them.
This policy permitted the US money supply to fall by over a third from 1929 to 1933.
When this money shortage caused runs on banks, the Fed maintained its true bills policy, refusing to lend money to the banks in the way that had cut short the 1907 panic, instead allowing each to suffer a catastrophic run and fail entirely.
This policy resulted in a series of bank failures in which one-third of all banks vanished.
According to Ben Bernanke, the subsequent credit crunches led to waves of bankruptcies.
Friedman said that if a policy similar to 1907 had been followed during the banking panic at the end of 1930, perhaps this would have stopped the vicious circle of the forced liquidation of assets at depressed prices.
Consequently, the banking panics of 1931, 1932, and 1933 might not have happened, just as suspension of convertibility in 1893 and 1907 had quickly ended the liquidity crises at the time.”Monetarist explanations had been rejected in Samuelson's work "Economics", writing "Today few economists regard Federal Reserve monetary policy as a panacea for controlling the business cycle.
Purely monetary factors are considered to be as much symptoms as causes, albeit symptoms with aggravating effects that should not be completely neglected."
According to Keynesian economist Paul Krugman, the work of Friedman and Schwartz became dominant among mainstream economists by the 1980s but should be reconsidered in light of Japan's Lost Decade of the 1990s.
The role of monetary policy in financial crises is in active debate regarding the 2007–2012 global financial crisis; see Causes of the 2007–2012 global financial crisis. 
Many economists have argued that the sharp decline in international trade after 1930 helped to worsen the depression, especially for countries significantly dependent on foreign trade.
Most historians and economists partly blame the American Smoot-Hawley Tariff Act (enacted June 17, 1930) for worsening the depression by seriously reducing international trade and causing retaliatory tariffs in other countries.
While foreign trade was a small part of overall economic activity in the U.S. and was concentrated in a few businesses like farming, it was a much larger factor in many other countries.
The average "ad valorem" rate of duties on dutiable imports for 1921–1925 was 25.9% but under the new tariff it jumped to 50% in 1931–1935.
In dollar terms, American exports declined from about $5.2 billion in 1929 to $1.7 billion in 1933; but prices also fell, so the physical volume of exports only fell by half.
Hardest hit were farm commodities such as wheat, cotton, tobacco, and lumber.
According to this theory, the collapse of farm exports caused many American farmers to default on their loans, leading to the bank runs on small rural banks that characterized the early years of the Great Depression. 
A Program for Monetary Reform was a proposal to return the American economy to full employment following the Great Depression.
It was written in 1939 by a group of academic economists and circulated within the academic community.