The political left’s love affair with steep progressive taxation received an academic boost with the publication of Thomas Piketty’s 2014 bestseller, Capital in the Twenty-First Century. Citing the New Deal era, Mr Piketty proposed a simple explanation and remedy for rising economic inequality: the concentration of income among the top 1% could be mitigated by strategically targeting wealth in the tax system.
Mr. Piketty based his theory on a historical argument from his own empirical work with fellow economist Emmanuel Saez. When Congress and President Franklin D. Roosevelt raised the top marginal tax rate to 91% during the New Deal and World War II, they supposedly broke the concentration of capital stock at the top of the income ladder. Inequality fell to a mid-century low, where it remained until the Reagan tax cuts of the 1980s. The disparity then rebounded, forming a centuries-old U-shaped pattern. So the solution is to bring tax rates back to FDR levels.
https://www.wsj.com/articles/inequality-picketty-saez-accounting-error-wealth-income-tax-capital-warren-aoc-ocasio-cortez-11649706037 Inequality and the Piketty Accounting Error