The last economic depression in the United States that did not result in massive government intervention was the collapse of 1920-21.

Judge by mainstream US economic history as of April 2009. True: historians generally describe the 1920–21 downturn as a severe depression met with little federal intervention (no large fiscal stimulus or bailouts; Fed policy mainly tightening or passive), and every later US downturn of depression-level severity (at least 1929–33 and 2008–09, and any others treated as depressions) involved massive government intervention. Mostly true: both points hold, but a minor detail is off, for example the Fed's role in 1920–21 is better described as significant but not massive, or the classification of 1920–21 as a 'depression' and not a severe recession is disputed. Mixed: the description of 1920–21 is accurate, but a later depression-scale downturn also saw little intervention, or the evidence on 1920–21 itself is split. Mostly false: 1920–21 had relatively limited intervention, but the claim's framing materially distorts the record, for example there was significant monetary intervention, or an earlier or later comparable episode better fits the description. False: the 1920–21 collapse involved massive government intervention, or later depressions clearly occurred without it.

Set before the research began.

1. E1 Not-So-Great Depression Cato Institute · 7 January 2009

   “Harding’s Secretary of Commerce Herbert Hoover wanted government intervention in the economy— which as president he was to pursue when he faced the Great Depression a decade later— but Harding would have none of it. He insisted that relief measures were a local responsibility.”

2. E2 Not-So-Great Depression Cato Institute · 7 January 2009

   “Federal spending was cut from $6.3 billion in 1920 to $5 billion in 1921 and $3.2 billion in 1922.”

3. E3 An Overview of the Great Depression EH.Net Encyclopedia (Randall Parker, East Carolina University) · 16 March 2008

   “Moreover, Eichengreen (1992) suggests that the episode of 1920–21 led the Federal Reserve System to believe that the economy could be successfully deflated or “liquidated” without paying a severe penalty in terms of reduced output.”

4. E4 Money, Sticky Wages, and the Great Depression Board of Governors of the Federal Reserve System (International Finance Discussion Paper 591, authors Bordo, Erceg, Evans) · September 1997

   “In particular, both the absolute severity of the Depression’s downturn and its relative severity compared to the 1920-21 recession are likely attributable to the price decline having a much larger unanticipated component during the Depression, as well as less flexible wage-setting practices during this latter period.”

The evidence indicates limited federal intervention in 1920–21, with federal spending cut and relief left to local authorities [E1][E2]. However, it does not show that every later depression-level downturn involved massive intervention: it has nothing on 2008–09, and for 1929–33 it says only that Hoover pursued intervention [E1].