As the rich world knows all too well, credit cards are as dangerous as they are convenient. With millions of consumers from China to Mexico filling their wallets with plastic, the risks are mounting as fast as people can say, “Charge it!”

The U.S. financial crisis cannot be contained. Indeed, it has already begun to infect other countries, and it will travel further before it’s done. From sluggish trade to credit crunches, from housing busts to volatile stock markets, this is how the contagion will spread.

For decades, politicians and political scientists have clung to the notion that free nations breed happy people. Now, though, a new ‘science of happiness’ is turning that equation on its head.