Unlike fossil fuels, this power source would not be subject to depletion. Vast tracts of land would be freed for agriculture—including the Sahara desert, which was to be irrigated with the help of three sea-sized man-made lakes throughout Africa. The massive public works, envisioned to go on for more than a century, would relieve unemployment and the acquisition of new land would ease the pressure of overpopulation, which Sörgel thought were the fundamental causes of political unrest in Europe.