Why has income inequality increased so much in the U.S. over the last 30 to 35 years?

Especially under Republican Presidents, taxation of the rich has been reduced considerably, to a level where many rich Americans have stated publicly that they think that they ought to contribute more. Corporate top salaries and bonuses have increased considerably over the last decades: where in the Seventies a corporate director might earn 100 times the amount of the lowest wages in a firm, that has now risen to 1,000 times and sometimes much more. At the same time, raising the legal minimum wage has over the decades mostly gotten stuck in the wheels of Washington politics. Recent studies have shown that today the chances for a child to raise himself above the social, educational and income level of his parents is considerably higher in Canada and many European countries than in the US