So says Michael Sivy for Time, here:
The income tax has always been hated – but so were the taxes it replaced. In Colonial America and the early U.S., taxes were typically on goods like sugar, tea, or whiskey (which triggered the Whiskey Rebellion in 1791). Other taxes were on land or were poll taxes (which was a flat amount per person and had nothing to do with voting). Later on, there were high custom duties on imports, which were one of the chief causes of the Civil War because they pushed up the prices of manufactured goods, helping the North but hurting the agrarian South. Real estate taxes were always extremely unpopular and still are.
It wasn't until 1863 when The War of Northern Aggression was going badly for Lincoln that it became officially about slavery.
