A century ago, on Feb. 3, 1913, the 16th Amendment to the Constitution authorizing a federal income tax was ratified. But the amendment’s adoption was more an accident than an act of political will, and tinkering with the Constitution was not even required for the federal government to tax Americans’ earnings. …

Before World War II, only one-third of the population earned enough to be subject to the income tax. After the war, the tax still affected only half the population. As late as 1947, farmers paid little or no income tax even when crops were good—it was generally accepted that they kept no books and were not expected to do much paperwork.

Over the years, the personal exemption and standard deduction have not kept pace with inflation, so today 70% of the population is subject to income taxes. Almost 60 million returns, mostly under $20,000 in gross income, pay no income tax, largely the result of the earned-income and child tax credits. The individual income tax today raises $950 billion annually through 144 million tax returns. Of this, the top 40 million returns pay about $856 billion and the bottom 104 million returns only about $94 billion.