Why did the German economy collapse in 1929?

The German economy was not 'in ruins throughout the 1930s'. Like most other countries it was hit by the Great Depression that followed the stockmarket crash of October 1929. It was affected more severely than, for example, Britain and for a while had an extremely high rate of unemployment in the early 1930s, like the U.S. By 1933 the economy was slowly picking up, thanks partly to measures initiated by the Weimar governments. After Hitler came to power in 1933 onwards the German economy received an enormous boost from rearmament. Unemployment fell and living standards rose, though there is disagreement about some of the details.