I can't speak from an historian's perspective, but I can explain the current state of economic thought.

Milton Friedman and Anna Schwartz's "A monetary history of the United States" fundamentally changed how we understood the Great Depression. Before Schwartz and Friedman, the Keynesian view was dominant: The Great Depression was caused by a shift in the aggregate demand curve, resulting in lower prices and lower output. (Are you familiar with the crossed lines graph of supply and demand? Aggregate demand is basically the sum total of all demand curves in the economy.) In other words, people suddenly stopped buying stuff, this resulted in producers slashing prices to clear out their stock and laying off workers because they couldn't sell as much as they could before, and people and businesses defaulted on loans which caused banks to go bankrupt and lower the supply of money, which meant ever larger numbers of people had less income to buy stuff... A death spiral. But why did people suddenly stop buying stuff? There's no real answer, definitely no theoretical answer. In economics terms it's an "exogenous shock," which means it's a change that came from outside of the system being modeled. This is where Keynes' famous term "animal spirits" comes from, people got spooked and stopped buying just like a herd of animals can get spooked and stampede for no apparent reason.

Friedman and Schwartz were able to identify the cause of the depression and show that the Keynesian aggregate demand model got the causality wrong. It turns out that the Federal Reserve implemented "tight money" policies that reduced the supply of money in the market. That led to prices falling (deflation)(1) and therefore companies laying off workers and producing less stuff and then people being unable to buy as much stuff. The government's actions, stimulus and whatnot, were largely irrelevant to what was happening to the economy because the depression was a fundamentally monetary phenomenon, i.e it was caused by too little money in circulation and wouldn't be resolved until enough money was added to get growth going again.

It took a while for this research to become fully accepted in the economic community, but follow up research vindicated Friedman and Schwartz, and it has become the generally accepted understanding that Federal Reserve policies caused the Great Depression. To the point that Ben Bernanke, then Chairman of the Board of the Federal Reserve and a noted Great Depression researcher himself, said "Let me end my talk by abusing slightly my status as an official representative of the Federal Reserve. I would like to say to Milton and Anna: Regarding the Great Depression. You're right, we did it. We're very sorry. But thanks to you, we won't do it again." (That whole speech is well worth reading as he goes through a more in depth treatment of Friedman and Schwartz's work and is understandable to a non-economist.)

Reference:

Friedman, Milton, and Anna Schwartz. "A monetary history of the United States." (1963).

(1) A note on how money, prices, inflation, etc tie together. There is an identity: MxV = PxY This states Money times Velocity of money (how long it takes money to be cycled through the economy) is equal to Prices times output. (Y is output in pretty much every econ model, from GDP to an individual firm's production function.) So, if the amount of money decreases, then the average price level and/or total output must also decrease in order to balance out the change. (It takes a pretty fundamental change to how the economy works in order to change the velocity of money.) The other side of the coin is, if output changes, money supply needs to change in the same direction in order to keep prices the same. This is why the Fed shoots for a constant 2% inflation: Deflation is capital B Bad, see the Great Depression. Also, output generally increases over time. So, they have to keep increasing the money supply to keep prices stable, but if they misjudge how much output increases they might not increase the money supply enough, which leads to deflation, so they give themselves a buffer by increasing the money supply more than they expect to need to based upon the increase of output.