Background on the Great Depression

And why it's relevant to the credit crisis today:

At the start of the 1930s, despite everything that had happened on Wall Street, the American economy had not yet collapsed. Consumer spending and business investment were down, but not horribly so.

In late 1930, however, a rolling series of bank panics began. Investments made by the banks were going bad — or, in some cases, were rumored to be going bad — and nervous customers besieged bank branches to demand their money back. Hundreds of banks eventually closed.

Once a bank in a given town shut its doors, all the knowledge accumulated by the bank officers there effectively disappeared. Other banks weren’t nearly as willing to lend money to local businesses and residents because the loan officers at those banks didn’t know which borrowers were less reliable than they looked. Credit dried up.

“If a guy has a good investment opportunity and he can’t get the funding, he won’t do it,” Mr. Mishkin, who’s now an economics professor at Columbia, notes. “And that’s when the economy collapses.” Or, as Adam Posen, another economist, puts it, “That’s when the Depression became the Great Depression.” By 1932, consumption and investment had both collapsed, and stocks had fallen more than 80 percent from their peak.

What does that mean for today?

The current fears can certainly seem irrational. Most households and businesses are still in fine shape, after all. So why aren’t some banks stepping into the void and taking advantage of the newly high interest rates to earn some profit?

There are two chief reasons. One is fairly basic: bankers are nervous that borrowers who look solid today may not turn out to be so solid. Think back to 1930, when the American economy seemed to be weathering the storm.

The second reason is a bit more complex. Banks own a lot of long-term assets (like your mortgage) and hold a lot of short-term debt (which is cheaper than long-term debt). To pay off this debt, they need to take out short-term loans.

In the current environment, bankers are nervous that other banks might shut them out, out of fear, and stop extending that short-term credit. This, in a nutshell, brought about Monday’s collapse of Wachovia and Glitnir Bank in Iceland. To avoid their fate, other banks are hoarding capital, instead of making seemingly profitable loans. And when capital is hoarded, further bank failures become all the more likely.

The crucial point is that a modern economy can’t function when people can’t easily get credit. It takes a while for this to become obvious, since most companies and households don’t take out big new loans every day. But it will eventually become obvious, and painfully so.

One example: car sales are plummeting.