@nun
We're depending on my memory here, so......
IIRC.....The income tax was introduced in 1861. Those resident in the 'Union' paid a flat fee of 3%(I think) on income from within the Union, while those who were non-resident (the dastardly cowards) paid 5% on income generated from sources within the Union. In 1864, the rules were revised for those non-resident, and the 5% was then applied, in addition to income from within the Union, to all income worldwide. Hence, the first application of where we are today. But, I could be wrong.
I researched my family to keep me busy when I first retired. I came across a document from one county where a relative, during the Civil War, had paid $0.06 tax on two hogs they had sold for slaughter. That side of the family were Yankees.
@Kelly85
You're not thinking of Texas are you?
During the Scottish Referendum earlier this year, Texas sent a delegation to Scotland to observe how the proceedings were organised.
During the Civil War, perhaps the Rebels felt they were airmailing a foreign tax to the Union via the scrap value of lead shot and cannonballs.