Things that make you go hum.
The Problem:
The Supreme Court's 1895 Pollock v. Farmers' Loan & Trust Co. ruling declared federal income taxes unconstitutional, as they were deemed "direct" taxes not apportioned by state population, as required by the Constitution.
The Solution:
Following years of advocacy by reformers, the 16th Amendment was ratified on February 3, 1913, bypassing the Pollock decision.
First Implementation:
The Revenue Act of 1913 followed, introducing a 1% tax on income over $3,000.
https://en.wikipedia.org/wiki/Sixteenth_Amendment_to_the_United_States_Constitution