Which statement accurately summarizes the history of marginal tax rates in the United States? Marginal tax rates were introduced after the Civil War and have been steadily increasing since that time. Marginal tax rates have been used since the Constitution was written and have never been above 50%. Marginal tax rates have been the basis for the U.S. tax code since the passage of the 16th Amendment. Rates have fluctuated, with the highest marginal tax rate as high as 94%. Marginal tax rates were introduced under Ronald Reagan's 1981 tax reform and have been steadily decreasing since that time