When World War I ended, the nations who won divided the spoils. The heads of state of the Allied nations made the decisions to make Germany pay for the cost of the war. Money was tight and other countries started squeezing Germany to pay its war debts. Germany couldn't pay. Everything tumbled out of control and the world economy collapsed.
History is like a tangled string.
Facts, opinions and memory come together. The fun is untangling the string. This one was a world depression. In the past, if there was a depression in the United States, Europe would buy American products because they were cheaper. During the Great Depression no country had enough money to invest to end the depression.