Why did world population begin to increase steadily after 1600?

A (still not understood) lessening of the mortality associated with epidemics, gradual agricultural improvement and (in Europe) social changes which encouraged production and opportunity, and (mostly from the eighteenth century) the impact of new crops from the Americas (the potato in Europe, maize and sweet potato in China). From the nineteenth century industrialisation, medical progress and the growth of American (and for a time Russian) food exports contributed to European growth.