Income tax return for taxation also vary, making comparisons all the more difficult. Countries that tax income generally use one of two systems: territorial or residential. In the territorial system, only local income – income from a source inside the country – is taxed. In the residential system, residents of the country are taxed on their worldwide (local and foreign) income, while nonresidents are taxed only on their local income. In addition, a very small number of countries, notably the United States, also tax their nonresident citizens on worldwide income. Countries with a residential system of taxation usually allow deductions or credits
Income tax in the United States direct tax on the basis of the source of the income. The Amendment removed the need for the income tax to be apportioned among the states on the basis of population. Income taxes are required, however, to abide by the law of geographical uniformity. Some tax protesters and others opposed to income taxes cite what they contend is evidence that the Sixteenth Amendment was never properly ratified, based in large part on materials sold by William J. Benson. In December 2007, Benson's "Defense Reliance Package" containing his non-ratification argument which he offered for sale on the Internet, was ruled by