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Bond drives using techniques invented by Jay Cooke during the Civil War were quickly implemented, now with the addition of using movie stars such as Douglas Fairbanks, Mary Pickford, and Charlie Chaplin to entice citizens into buying Liberty Bonds. And the income tax, which had been a mere social-engineering device to get the rich to share more of the tax burden, began to bite into the middle class. The personal exemption, which had been at $3,000, was dropped to $1,000. The tax rate, a mere 7 percent on incomes more than $500,000 before the war, rose to 77 percent. The income tax thus became the most important source of federal revenues, as it has remained ever since. And this changed the nature of the endless debate over taxes.
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John Steele Gordon (An Empire of Wealth: The Epic History of American Economic Power)