The Economist’s “schools briefs” on the financial crisis: Parts 1, 2, 3, 4, 5. Quoting from the first part:

… it is clear the crisis had multiple causes. The most obvious is the financiers themselves—especially the irrationally exuberant Anglo-Saxon sort, who claimed to have found a way to banish risk when in fact they had simply lost track of it. Central bankers and other regulators also bear blame, for it was they who tolerated this folly. The macroeconomic backdrop was important, too. The “Great Moderation”—years of low inflation and stable growth—fostered complacency and risk-taking. A “savings glut” in Asia pushed down global interest rates. Some research also implicates European banks, which borrowed greedily in American money markets before the crisis and used the funds to buy dodgy securities. All these factors came together to foster a surge of debt in what seemed to have become a less risky world.