The causes of 1990-91 and 2007-09 were similar: Real estate collapse, stock market turbulence, financial engineering turkeys come home to roost, loan failures, taxes going up, a Middle Eastern war, a spike in oil prices and everybody de-leveraging at once.

FORBES: Great Recession Did Not Have To Be Great

In the 1991 Gulf war, the conflict was over swiftly and the oil-price spike short-lived, so the markets soon recovered.

ECONOMIST: How low could they go? | The

Another synchronous round of QE, for instance, may end up causing a trade war, while an additional debt-financed fiscal stimulus could cause a spike in interest rates.

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The long post-World War II bull market in stocks ended during the 1966 to 1969 era when the rate of inflation began to spike.

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