The Answer:

According to the History of the Income Tax in our almanac, the federal income tax was first enacted in 1862 to support the Union's Civil War effort. It was eliminated in 1872, revived in 1894, then declared unconstitutional by the Supreme Court the following year. In 1913, the 16th Amendment to the Constitution made the income tax a permanent fixture in the U.S. tax system.

—The Editors