The causes of the Great Depression are still a matter of discussion/controversy, a useful indicator of the complexity of the modern credit-economy. My general sense is that mass consumer credit and stock margin debt were relatively new phenomena in the 1920s and so credit on a relative basis expanded mightily. Enough of this credit went into marginal assets such as stocks and farmland that was only productive in short-lived eras of ample rainfall that when leverage had to be reduced and liquidity tightened, the collateral was only worth a fraction of the debt.
I read somewhere that some of the debt accumulated in the Roaring 20s wasn’t written down until the early 1950s. In other words, authorities kept the debt on the books, much as Japan has done since 1990, institutionalizing stagnation.