Why Income Tax?
How did income tax become the convoluted behemoth it is today?
Income taxes have never been un-Constitutional, but before the 16th Amendment the funds had to be distributed among the States based on the results of the Census.
While the 16th Amendment gave the government great leeway in determining how tax dollars could be used, at first it used that power to just tax a very small amount on large incomes.
But the poor timing of this Amendment being ratified came as World War I broke out. It was this and all wars afterwards that further expanded income tax as the default choice for the Federal Government.