NEW YORK — In September 2008, the global economy and financial system was hit by an earthquake, whose epicenter was in the United States. It was the end of the Bush administration. The presidential election was two months away. The timing, from the point of view of crisis management, could not have been worse.

The level of uncertainty about asset values, solvency and the connectedness of balance sheets that prevailed at the time was extraordinarily high. Uncertainty bred fear, causing banks, businesses and households to hoard cash. Consumption plummeted, taking down retail sales with it and, after a short lag, employment and investment as well. Individually rational choices were giving rise to collectively irrational results.

These conditions had all the makings of a depression scenario, with credit rationing destroying businesses indiscriminately, and thus required fast, aggressive and unconventional action by the U.S. government and the Federal Reserve. The response, mounted by the Bush administration and taken over by the Obama administration, was all of the above. A combination of financial-sector recapitalization and rapid expansion of the Fed's balance sheet prevented a complete credit lockup.