Between 1919 and 1920:
- America's gross national product (GNP) grew from $78 billion to $103 billion.
- The number of households with a radio rose from 60,000 to 10 million.
- The number of people filing income tax returns for earnings of more than $1 million a year rose from 65 to 513.
- The number of airline passengers grew from less than 6000 in 1926, to approximately 173,000 in 1929.
Five causes of the boom
- solationism- the republican government under President Harding (1921-3) and President Coolidge (1923-9) kept out of foreign affairs, and limited foreign competition by imposing high import tariffs.
- Technology- especially in the electrical, chemicals…