Tragically, in most of sub-Saharan Africa, standards of living were lower 20 years after the imperialists were gone. In Central Asia likewise, freedom from Russian domination after the break-up of the Soviet Union did not bring rising standards of living but falling standards of living. Most of the scientific, technological, and managerial skills in Central Asia did not belong to Central Asians but primarily to Russians. In medieval Europe, Jews were expelled from a number of countries where they were accused of exploiting the gentiles. But, after they left, prices and interest rates tended to rise.
Exploitation does take place and oppression still more so.
But they seldom explain either the wealth of the wealthy or the poverty of the poor. Spain, for example, exploited the Western Hemisphere and its people mercilessly for centuries. But after the gold and silver ran out and the Indians died off, Spain had very little to show for it and has remained one of the poorer countries in Europe. It not only failed to develop its own human capital, it expelled minorities whose human capital had contributed to the Spanish economy, including both the Jews and the Moors. Although human capital fits the facts better than moral melodrama, it presents no sweeping solutions for politicians to offer and no heady feeling of superiority for the intelligentsia.