Yes of course income tax was imposed as you state, but did you understand that payroll withholding of that tax was imposed in 1943 as I stated? Before that, everyone paid their taxes at the end of the year with their tax return? They got it approved without a whimper by the populace because "it was for the war". Did you understand that point?
Here's another point to add. At first, the federal income tax only applied to Federal employees/contractors, which means 99% of america didn't pay income taxes. Some argue that the law was never changed to include non-federal employees and at some point (maybe after the war, or maybe it changed in 1943 - I don't know the dates) all americans started paying taxes, though, they argue, this is illegal. Many people who are part of the "I won't pay federal taxes" movement file amended federal returns and get all their money back for the prior 10 years of their life. And the IRS doesn't flinch a bit; they send back the money.
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Being i've worked in the tax industry in the past, they have some valid arguments. When you fill out a W4 form when you start working at a company, there is language which states that you are declaring that you are agreeing to have taxes withheld from your paycheck per the IRS rules on federal employee. Since we all unknowingly agree to this, and sign this legal docuмent, then we are implicitly stating that we are federal employees (when obviously we are not). This puts us legally "in the system" and thus, we have to pay taxes.
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Many who go to court over failing to pay taxes argue that they aren't federal employees and don't have to pay. Interestingly, the IRS avoids this argument like the plague (cause they know it's true, and easily provable per the IRS codes and even Supreme Court rulings). They will argue that once you fill out a W4 you are obligated to pay (and corrupt judges will agree). It's just another example of legal trickery that the system has used to trap America into something that is unconstitutional.