The big bad leverage monster. Remember how the 1929 stock crash was caused in large part by investors speculating on stocks using margin (borrowing) to leverage their bets? See if this sounds familiar::

In the equities-market downturn early in this decade, declining assets were held by institutional and individual investors that either owned the assets outright, or held only a small fraction on margin, so losses were absorbed by their owners. In the current crisis, declining housing assets were often, in effect, purchased between 90% and 100% on margin. In some of the cities hit hardest, borrowers who purchased in the low-price tier at the peak of the bubble have seen their home value decline 50% or more. Over the past 18 months as housing prices have fallen, millions of homes became worth less than the loans on them, huge losses have been transmitted to lending institutions, investment banks, investors in mortgage-backed securities, sellers of credit default swaps, and the insurer of last resort, the U.S. Treasury.

That’s a clear, succinct explanation of the magnitude of the crisis and why it’s grievously wounded the financial system.

But the economists try to poke through that theory of the Depression’s cause, as well as Milton Friedman’s and Anna Schwartz’s famous monetary theory of the cause:

The Great Depression has been attributed to excessive speculation on Wall Street, especially between the spring of 1927 and the fall of 1929. Had the difficulties of the banking system been caused by losses on brokers’ loans for margin purchases in 1929, the results should have been felt in the banks immediately after the stock market crash. But the banking system did not show serious strains until the fall of 1930.
Bank earnings reached a record $729 million in 1929. Yet bank exposures to real estate were substantial; as the decline in real estate prices accelerated, foreclosures wiped out banks by the thousands. Had the mounting difficulties of the banks and the final collapse of the banking system in the “Bank Holiday” in March 1933 been caused by contraction of the money supply, as Milton Friedman and Anna Schwartz argued, then the massive injections of liquidity over the past 18 months should have averted the collapse of the financial market during this current crisis.

And they make a parallel between the Depression:

The events of the past 10 years have an eerie similarity to the period leading up to the Great Depression. Total mortgage debt outstanding increased from $9.35 billion in 1920 to $29.44 billion in 1929. In 1920, residential mortgage debt was 10.2% of household wealth; by 1929, it was 27.2% of household wealth.

They blame the Great Depression on a great consumer-debt washout similar to what we’re going through now.

The hypothesis we propose is that a financial crisis that originates in consumer debt, especially consumer debt concentrated at the low end of the wealth and income distribution, can be transmitted quickly and forcefully into the financial system. It appears that we’re witnessing the second great consumer debt crash, the end of a massive consumption binge.

We have a long, hard slog ahead of us.

The problem I have with this consumer-debt theory is that they don’t mention how levered the banking system is, too. One follows the other. If the banks hadn’t been able to lever themselves so much, consumers wouldn’t be in so much debt, but it’s turned out it didn’t have the capital to make those loans.

Still, it’s a worthy piece.

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Ryan Chittum is a former Wall Street Journal reporter, and deputy editor of The Audit, CJR's business section. If you see notable business journalism, give him a heads-up at rc2538@columbia.edu. Follow him on Twitter at @ryanchittum.