Since 1913 a progressive federal income tax system has been in place, with tax rates increasing as income rises. The top marginal tax rates resulting from the costs incurred by World War I were at, or about, 70%. From 1925-1931, the years leading up to and including part of the Great Depression, the top rate was 25%. Where was our booming economy when top rates were that low? That ought to tell us something!
During World War II, tax rates for the wealthiest of Americans soared, reaching 94 % in 1944 and 1945. Similarly, the top tax rates during and following the Vietnam war were at 91% over a period of many years.
As a result of President George W. Bush's tax cuts, the current top tax rate is among the lowest ever at 35%. Taxes on unearned income (investments, stocks, bonds, etc.) also are at historically low levels.