"The various durations of government around the world are linked to the various durations and productivities of farming that was the prerequisite for the rise of governments. For example, Europe began to acquire highly productive agriculture 9,000 years ago and state government by at least 4,000 years ago, but subequatorial Africa acquired less productive agriculture only between 2,000 and 1,800 years ago and state government even more recently. Those historical differences prove to have huge effects on the modern distribution of wealth. Ola Olsson and Douglas Hibbs showed that, on average, nations in which agriculture arose many millennia ago—e.g., European nations—tend to be richer today than nations with a shorter history of agriculture (e.g., subequatorial African nations), and that this factor explains about half of all the modern national variation in wealth. Valerie Bockstette, Areendam Chanda, and Louis Putterman showed further that, if one compares countries that were equally poor fifty years ago (e.g., South Korea and Ghana), the countries with a long history of state government (e.g., South Korea) have on the average been getting rich faster than those with a short history (e.g., Ghana)."