The Great Depression was a severe worldwide economic depression that took place mostly during the 1930s, beginning in the United States. The timing of the Great Depression varied across the world; in most countries, it started in 1929 and lasted until the late 1930s. It was the longest, deepest, and most widespread depression of the 20th century.
Source : Wikipedia
Despite its enormity and historical importance, the causes of the depression are still being debated almost a century later.
To understand the Great Depression is the Holy Grail of macroeconomics. Not only did the Depression give birth to macroeconomics as a distinct field of study, but also - to an extent that is not always fully appreciated - the experience of the 1930s continues to influence macroeconomists' beliefs, policy recommendations, and research agendas. And, practicalities aside, finding an explanation for the worldwide economic collapse of the 1930s remains a fascinating intellectual challenge."
Ben Bernanke, Journal of Money, Credit and Banking.
There are more than a dozen mainstream theories which attempt to make sense of the crash. None has yet been generally accepted as providing a full explanation.
Without a complete understanding of the depression, it seems unlikely that macro-economists will be able to recommend global structural economic reforms and strategies which might help to prevent a modern-day re-occurrence.
See Causes of the Great Depression at Wikipedia.
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