There have been periodic depressions throughout U. S. History, the depression that started in 1929 is called the Great Depression because it affected so many people for so long. What caused the Great Depression? No one knows for sure but the stock market crash of 1929 marked its start. Learn many things about the Great Depression and the 1920s with this kit of 26 KIDS DISCOVER magazines, teacher's guide and Power Vocabulary guide with student handouts.