What caused the economic depression after World War 1?

Due to the cost of WWI for all the countries involved many didn't have enough money to pay back countries that they had borrowed from during the war. Each country involved had their own war debt to pay and in Germany's case not only their own debt but the debt of all other European contries due to the agreement in the Treaty of Versailles. During this period of time in history the Industrial Revolution tied many countries, especially those that were Imperialists, together. In a sense the beginning of the global economy had began. This type of economy ties each country in the global economy together and therefore when one countries economy is suffering a domino type of effect occures, and each country tied to the affected economy will suffer in some way.