gold, page-54166

And here's the other main reason for the Great Depression.

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The gold standard.
Whatever its effects on the money supply in the United States, the gold standard unquestionably played a role in the spread of the Great Depression from the United States to other countries. As the United States experienced declining output and deflation, it tended to run a trade surplus with other countries because Americans were buying fewer imported goods, while American exports were relatively cheap. Such imbalances gave rise to significant foreign gold outflows to the United States, which in turn threatened to devalue the currencies of the countries whose gold reserves had been depleted. Accordingly, foreign central banks attempted to counteract the trade imbalance by raising their interest rates, which had the effect of reducing output and prices and increasing unemployment in their countries. The resulting international economic decline, especially in Europe, was nearly as bad as that in the United States.