The progressive income tax was made possible by which amendment?

The progressive income tax was made possible by the 16th Amendment to the United States Constitution. Ratified in 1913, this amendment granted Congress the power to levy and collect taxes on income without apportioning it among the states or basing it on the U.S. Census. This was a significant shift in the federal government's ability to generate revenue, allowing for a tax system that could adjust rates based on income levels. The introduction of a progressive income tax aimed to reduce economic inequality by taxing higher incomes at higher rates, thus emphasizing the principles of fairness and equity in taxation.

The other amendments listed do not pertain directly to the establishment or authorization of an income tax. The 17th Amendment dealt with the direct election of senators, the 18th Amendment introduced Prohibition, and the 19th Amendment granted women the right to vote. None of these amendments influence the taxation system in the same way that the 16th Amendment does.