Question

why was the depression of 1929 known as Great Depression

Answer 1

Economic historians usually attribute the start of the Great Depression to the sudden devastating collapse of U.S. stock market prices on October 29, 1929, known as Black Tuesday. Even after the Wall Street Crash of 1929  optimism persisted for some time.
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Answer 2

Economic historians usually attribute the start of the Great Depression to the sudden devastating collapse of U.S. stock market prices on October 29, 1929, known as Black Tuesday. ... Even after the Wall Street Crash of 1929 optimism persisted for some time.