From 1929 until World War II, most of the world suffered extraordinary economic problems.
Real output falls even more.
In the U.S., the downturn began in 1929, and got much worse from 1931-1933. The economy slowly recovered over the next 8 years. It fell again in 1937-8. The same happened all over the world. The monetary decline and the depression in the U.S. were not especially severe until 1931.