The "Great Depression" was NOT a singular thing; but rather multiple things in succession (each with their own root causes, as well as aggravating factors).
The root cause was the creation of the Federal Reserve in 1913.
The crash of 1929 was undoubtedly caused by the Fed and the credit expansion of the late 1920's -- the speculative "boom" created to AVOID the recession (i.e. there SHOULD have been a minor "recessionary" correction in the mid 20's to correct for the post-war expansion -- the fact that the recession was delayed by a false inflation created the "bubble" with then burst). BTW Bernanke acknowledges that the Fed itself WAS the cause of this (indeed it's his academic "claim to fame" in economics).
The recession that followed in the early 30's was in part caused by the "reaction" of the Hoover "interventionist" administration -- including Fed policies as well as the Smoot-Hawley tarriffs, which were passed in mid June of 1930 (i.e. Ben Stein and others are being disingenuous when they "imply" that Smoot-Hawley caused the 29 crash).
The DEEPENING of the depression in 1933-34 and the years following can be laid directly at the feet of FDR, and his asinine "populist/fascist" demogogery against "capitalists" and "hoarders." His actions (illegal, unconstitutional, and unprecedented) in temporarily closing banks, confiscating gold, and then (almost immediately... within 6 months)
***DEVALUING the currency by 69% (the change in the "fixed" exchange rate from 1 0z Gold = $20 to 1 0z Gold = $35) caused a lot of people to pull back even further.
Note: The "BIG Boost" in the GDP during the 1934..37 era shown in most charts and attributed to the "New Deal" programs like TVA and NRA, etc. was actually the result of accounting fraud -- most of the charts do NOT normally adjust for the devaluation (and NONE of the charts and numbers produced by FDR's administration did -- "accounting for inflation" was not considered relevant at the time); those modern charts that do account for it (like the one below) digress from previous accepted practice by including government expenditures (prior to the "Keynsesians" government expenditures were NOT considered part of GDP). if you remove GOVERNMENT SPENDING from the various "New Deal" programs, the GDP actually went down significantly; as would be expected with the institution of socialist/fascist wage & price control schemes.
The "New Deal" had effectively failed by 1937 & 1938 (unemployment rates were at 14.3% in 1937 and reached 19.0% in 1938 -- and keep in mind this was PRE-feminest era, at that time unemployment really only meant ADULT MEN, nearly 1/2 of our "modern workforce" being stay-at-home wives and mothers).
The subsequent "boomlet" in the 1938..1940 era was mainly as a result of increased government spending -- FDR's only remaining option was War (and he knew it) --so the Lend-Lease act and the extensive pre-war military buildup (literally HUNDREDS of warships were built pre-1941, and
the draft was instituted in September of 1940 ... but
that is simply not taught in US Government schools... nor indeed is it even "spoken of" despite the plethora of evidence -- at least by not anyone other than Pat Buchanan; it sort of spoils the whole "Greatest Generation" BS).
In other words, FDR not only caused the "Great" part of the great depression, but essentially "cooked the books" and prepared the ground for war to cover his tracks and in an attempt to salvage himself and his administration. (Asimov's quote
"Violence is the last refuge of the incompetent" seems apropos).
The United States actually BECAME a progressively more "fascist" state during the New Deal, pre-war and WWII era. (Few people are truly aware of the extent to which the government under FDR literally "seized control" over factories, farms, etc. Virtually everything was put on a "war footing" with nearly all production -- in a mirror to Germany & Britain -- aimed at producing government spec'd and purchased goods. Many, indeed most "consumer goods" were eliminated or minimized, and then rationed by government fiat.)
On a psychological level, the population endured this forced deprivation out of a sense of patriotic fervor, which was fed by immense amounts of propaganda (Hollywood did "its part" in preparing peoples' psyche's ...even pre-war).
This "enforced deprivation" (and thus enforced savings and "hoarding" of currency -- the very thing FDR had despised just half a decade earlier) eventually created what is called a "pent up demand" (for everything from clothing to housing to automobiles and appliances) that later fueled the post-war boom.
Since FDR himself had died, he was unable to oversee the final phase of his "socialist/fascist dream" (we have only the writings of Elanor concerning the "plan" to keep conscription as an ongoing tool, but with draftees forced to serve terms in something like the current "AmeriCorps" -- but with a much larger and wider mission).
With the "boom" a quasi-natural form of inflation set in (over 6% in a single month in 1946) -- this was really simply a delayed implementation of the debt-financing that had taken place during the war years (and SHOULD have been expected). Significant strikes set in (including the nationwide railway strikes, plus the later coal mining strikes, etc) as a direct consequence, and Truman acted in a unilateral and fascist manner (in the end resorting to military force against citizens).
In opposition to Truman, the Taft faction of the Republican party was able to bring a small measure of sanity by instituting significant tax cuts, and removing the debilitating price and wage controls (but also unfortunately, via FDR-like unconstitutional expansion of Federal Government powers -- creation of NLRB, expansion of Federal Judicial oversight, etc -- but in favor of corporations versus the labor unions favored by FDR's socialism/populism.)
The economy grew (in part financed via government debt), but with the private sector utilizing the "surplus" of large-scale industrial machinery infrastructure leftover from the war-created to good advantage in creating peacetime equipment. (Much as in post devolution Russia, Ukraine and the Balkans, private industry has "salvaged" and reallocated a lot of the poorly-managed industrial infrastructure built up during the Soviet years).
The nation began paying off the debt from WWII, and was even able to handle the debt from the subsequent "military-industrial complex" and the Korean and Vietnam conflicts... but when LBJ added his own debt-financed "Great Society" (the "guns & butter" debates) the financial system began to fracture.
The dollar was being held to an artificially high fixed exchange rate versus Gold, and much of the world began to see this, causing foreign investors and governments to "do a run" on the American currency (called the "Balance of Payments Crisis") -- which forced a choice on Nixon: either have the Federal Government "fess-up" to reality and as a result, dramatically CUT government spending (military AND social) and reduce the size and scope of the Federal Government... or declare bankruptcy (in essence).
Nixon chose the latter -- and (via yet another unconstitutional and illegal FDR-like "Executive Order") he "temporarily suspended" redemption of the dollar into gold, and gave us the full-blown FIAT dollar system we have today.
...and that basically set the stage for where we have been ever since. During the 37 years since Nixon's unilateral "temporary" suspension of the gold-standard (done without ANY legislation, much less constitutional amendment) -- the dollar has tumbled to (approximately) less than 1/30 (perhaps less) of it's "fixed" value in mid 1971.
And along the way that FIAT currency has been the root and sole cause of the various "crises" -- like the "inflation crisis" and the "energy crisis" in the mid 1970's -- and allowing the various administrations (whether Republicrat or Demopublican) to repeat FDR's sleight-of-hand "cooking of the books" and engage in blame-shifting onto whoever is convenient -- whether those "nasty greedy OPEC Arabs" or those "cunning Japanese" -- or soon those "craft Chinese and Indians."
Sure people are now "aware" of inflation... but it is seen as some type of "naturally occurring phenomenon" -- as witness Bernanke's recent euphemistic testimony before Congress -- the blame still gets shifted elsewhere.
*** Personally I think the psychological effect on the populace (or at least that frugal portion that saved/invested) of that confiscation and SIGNIFICANT devaluation is severely UNDER-estimated (in fact it is wholly IGNORED in nearly all of the academic literature regarding the Depression).
Think of how the change in the CURRENT populations spending habits was affected "psychologically" by both the BOOM in housing values and it's current BUST...
Now consider the effect on a population where such a DEFINITE and SIGNIFICANT, unilateral and totally unexpected "devaluation of wealth" (effects of which included individual's savings, PLUS previous contracted wage agreements, landlord's rental contracts, and the HUGE number of business' contracts) -- with the remote possibility that it will be REPEATED in a similar fashion, again by the "arbitrary" decision of the government; how willing would YOU be to sign any contracts denominated in dollars?
In essence, the populations' "confidence" in the economy was gone. Like turtles, they retracted into their shells. Is it any wonder that it took YEARS for recovery to happen? Especially with a "chaotic" government passing a helter-skelter varioety of "alphabet soup" agencies that change emphasis from one month to the next?
To understand HOW DEBILITATING any devaluation of a currency can be to a society, one simply need to look at those countries that have undergone hyperinflation (how it affects businesses is nicely encapsulated in the "Hyperinflation Survival Guide" by Gerald Swanson -- the only book of its kind that I know of.) Note that the logic of our modern era "just-in-time"/"zero-inventory" is the opposite and indeed the WORST set of practices for a hyperinflation (or devaluation-prone) currency environment; hence the boom in "commodities" the antithesis of J-I-T thinking.[/indent]