The view that geographic factors such as climate, natural resources, disease burden or soil quality directly explain why some countries are poor still has many proponents. But these diehard geographic determinists notwithstanding, most people recognize that such geographic factors cannot explain world inequality today.
That being said, the dominant explanation about world inequality at the start of the early modern period (around 1500) is all about geography. This explanation, developed and popularized in Jared Diamond’s Guns, Germs and Steel, links inter-continental inequality circa 1500 to the historical distribution of domesticable animal and crop species. Where there were a lot of these the Neolithic Revolution — the transition from hunting and gathering to herding and farming — happened earlier and was more productive. In these places population density took off, and this spurred both technological progress and the emergence of complex societies.