The NYT's Paul Krugman offers his assessment of why the U.S. financial system is coming perilously close to going off the rails -- again.

He began by explaining how things went wrong in the 1929-1931 period, how the U.S. Congress subsequently passed laws to prevent the same situation from happening again -- and how Wall Street manoeuvred around those restrictions.

From the NYT:

Wall Street chafed at regulations that limited risk, but also limited potential profits. And little by little it wriggled free — partly by persuading politicians to relax the rules, but mainly by creating a “shadow banking system” that relied on complex financial arrangements to bypass regulations designed to ensure that banking was safe.

For example, in the old system, savers had federally insured deposits in tightly regulated savings banks, and banks used that money to make home loans. Over time, however, this was partly replaced by a system in which savers put their money in funds that bought asset-backed commercial paper from special investment vehicles that bought collateralized debt obligations created from securitized mortgages — with nary a regulator in sight.

As the years went by, the shadow banking system took over more and more of the banking business, because the unregulated players in this system seemed to offer better deals than conventional banks. Meanwhile, those who worried about the fact that this brave new world of finance lacked a safety net were dismissed as hopelessly old-fashioned.

In fact, however, we were partying like it was 1929 — and now it’s 1930.

The financial crisis currently under way is basically an updated version of the wave of bank runs that swept the nation three generations ago. People aren’t pulling cash out of banks to put it in their mattresses — but they’re doing the modern equivalent, pulling their money out of the shadow banking system and putting it into Treasury bills. And the result, now as then, is a vicious circle of financial contraction.

Mr. Bernanke and his colleagues at the Fed are doing all they can to end that vicious circle. We can only hope that they succeed. Otherwise, the next few years will be very unpleasant — not another Great Depression, hopefully, but surely the worst slump we’ve seen in decades.

Even if Mr. Bernanke pulls it off, however, this is no way to run an economy. It’s time to relearn the lessons of the 1930s, and get the financial system back under control.