The Constitution forbade Congress to tax land or people unless the taxes were apportioned according to the population of each state. Before 1913 all federal revenue came from tariffs on imports, excise taxes, or selling of public land. In the 1790s Congress had taxed carriages, but the Supreme Court ruled that it was not a direct tax, but an excise tax. During the Civil War, the United States government needed to raise money and taxed the incomes of professionals, such as lawyers, who earned over $1,000 each year. This tax lasted until 1872, and in 1881 the Supreme Court ruled that it had been constitutional.

Changing Circumstances.

In the 1870s and 1880s agitation grew for a new tax on incomes. In the 1780s most Americans lived on farms and could not measure annual income in dollars. One hundred years later the economy had changed. The disparities of...