The great depression started in the U.S., but it wasn’t created on purpose. After WW1 European countries were in bad shape and needed to rebuild. The U.S. came to the rescue and started loaning them money.
It worked, Europe slowly started to recover.
However, when the U.S. stock market collapsed in 1929 all of a sudden nobody had any money in the
0.S. Because of this they stopped lending money overseas and started asking for interest payments. Since Europe had not recovered yet they fell into a depression too.
With the U.S. and European economies collapsing they stopped importing things. Other countries (Like Canada and Australia) that depended on exporting goods to those two large marketplaces suddenly lost most of their businesses and jobs.
Basically the world is always intertwined, even today. But in the 1920s the world economy was largely dependent on how the U.S. did.
