For the past forty years western economies have splurged on debt. Now, the reality dawns that many debts cannot be repaid. But the oncoming defaults have a time-worn place in our economic history. As with crises in the 1930s and 1970s, governments will fall, currencies will lose their value, and new systems will emerge. Just as Britain set the terms of the international system in the nineteenth century, and America in the twentieth century, a new system will be set by today's creditors in...