Personal income tax is a tax imposed on a person that changes based on how much income the person receives. This type of tax is considered to be a progressive form of taxation because the tax rate increases as one's income increases. Interestingly enough, personal income taxes have not always existed in the United States.
 
1781 to 1789
The writers of the Articles of Confederation did not support a strong federal government. Thus, under the Articles (ratified on March 1, 1781), only state governments had the power to tax. In turn, however, states were required to turn over tax revenues to the federal government. Then, on June 21, 1788, the federal government gained new, stronger powers to tax citizens directly with the ratification of the U.S. Constitution (which replaced the Articles of Confederation). During this time period, the only taxes that existed were tariffs and excise taxes, but these provided ample revenue to the federal government for many years. Tariffs and excise taxes are known as regressive taxes because individuals with lower incomes pay more of their share of income in taxes relative to those with higher incomes.
 
1861 to 1872
During the Civil War, the federal government needed much more revenue than both tariffs and excise taxes could provide. Thus, on August 5, 1861, President Abraham Lincoln imposed the first federal tax on income by signing into law the Revenue Act. Shortly after the war, however, Congress repealed the Act. 
 
1909 to Present
The industrialization and modernization that occurred in the period following the Civil War (known as the "post-construction era") led to huge gains in personal wealth and fortunes that were not subject to tax at all. This inequity in the tax system led to the ratification of the Sixteenth Amendment, which gave Congress the "power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration." As a result, people with higher incomes paid more in taxes than those with lower incomes.

Personal income tax rates have varied dramatically throughout history, from rates as low as 1% in the early days to rates that exceeded 90% during World War II. In creating taxes, lawmakers attempt to balance the following goals: (1) building revenue; (2) influencing people’s spending habits; and (3) being fair to all taxpayers. The last major overhaul of the federal tax code was the enactment of the Tax Cuts and Jobs Act in 2018.