Answer:
do you want me to use the stats or what?
While the October 1929 stock market crash triggered the Great Depression, multiple factors turned it into a decade-long economic catastrophe. Overproduction, executive inaction, ill-timed tariffs, and an inexperienced Federal Reserve all contributed to the Great Depression.
I believe the process you are looking for would be urbanization.
By force. The Spartan soldiers would make annual raids/attacks on the Messenian Helots mainly to threaten them into submission, but also as military practice.