America's involvement in World War II had a significant impact on the economy and workforce of the United States. ... Our involvement in the war soon changed that rate. American factories were retooled to produce goods to support the war effort and almost overnight the unemployment rate dropped to around 10%.
The major causes of World War II were numerous. They include the impact of the Treaty of Versailles following WWI, the worldwide economic depression, failure of appeasement, the rise of militarism in Germany and Japan, and the failure of the League of Nations.
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