"[President Hoover] has many times declared that we are in a depression that is only part of a world depression...Hoover, all through 1931, quite naturally, adopted an explanation that located the cause of the Depression well beyond his reach. After all, presidents are only human. Most presidents who have suffered [economic] depressions in their administrations have blamed them on world conditions. The Democrats blamed Harrison's tariff for the depression of 1891. But Harrison said this measure had 'been in some degree checked by the surprising and very unfavorable monetary events in England.' In 1893, when the panic deepened, Clevland's friends insisted it was due to the world conditions he could not alter. In 1907 Roosevelt was charged with producing a panic with his anti-trust crusades. He replied: 'I don't care what they say. It's not true. Anyhow, the depression has been caused by world conditions.' Wilson's trade and money reforms were blamed for the depression of 1913. He denied it and said, 'The country is suffering from disturbances in Europe, chiefly due to the Balkan Wars and the repercussions of these wars in various countries in Europe.'"
President Hoover blamed the economic turndown on the First World War - you can be read more on this topic here...
