The book studies how international contest of military prowess, economic capability and overall national power works as a selection mechanism that prompts the replacement of nonperforming economies and institutions by the good ones. With the help of a mathematical model, the book studies how military technology interact with geography to determine the type of the international system, the degree to which the law of the jungle operates within the system and, the preference, behaviour and economic performance of the constituent states. The book applies the insights derived to analyse cases of very long term changes in economic performance from the past three millenniums of world history. When there are great economies of scale in military technology and a rough parity of capability between the international competitors, this selection mechanism works strongly. The law of the jungle drives nations to take their relative military, economic and overall capability seriously. Nations therefore strive to have good governance, reforms and innovations in institutions and other areas, and policies for achieving a strong military and a prospering economy.