Authority for the new sanctions, as with so many other policy weapons, comes from the USA Patriot Act, which in Section 311 authorizes Treasury to designate foreign financial institutions that are of "primary money laundering concern." Once a foreign bank is so designated, it is effectively cut off from the U.S. financial system. It can't clear dollars; it can't have transactions with U.S. financial institutions; it can't have correspondent relationships with American banks.

The new measures work thanks to the hidden power of globalization: Because all the circuits of the global financial system are inter-wired, the U.S. quarantine effectively extends to all major banks around the world. As Levey observed in a recent speech, the impact of this little-noticed provision of the Patriot Act "has been more powerful than many thought possible."

Treasury applied the new tools to North Korea in September 2005, when it put a bank in Macao called Banco Delta Asia on the blacklist. There was no legal proceeding — just a notice in the Federal Register summarizing the evidence: Banco Delta Asia had been providing illicit financial services to North Korean government agencies and front companies for more than 20 years, according to the Treasury notice. The little Macao bank had helped the North Koreans feed counterfeit $100 bills into circulation, had laundered money from drug deals and had financed cigarette smuggling. North Korea "pays a fee to Banco Delta Asia for financial access to the banking system with little oversight or control," Treasury alleged.

Wham! The international payments window shut almost instantly on Pyongyang's pet bank. Transactions with U.S. entities stopped, but the Treasury announcement also put other countries on notice to beware of Banco Delta Asia. The Macao banking authorities, realizing that they needed the oxygen of the international financial system to survive, took regulatory action on their own and froze the bank's roughly $24 million in North Korean assets. And around Asia, banks began looking for possible links to North Korean front companies — and shutting them down.