The key to the major changes that have occurred in the world system of societies in the last 10,000 years is the process of intersocietal selection that has drastically reduced the number of societies.  Were it not for this process, in which the units that survive (or become extinct) are entire societies, human life would not have change nearly as rapidly as it has (1991, p. 63).

Not all the differences that have developed among societies have been equally important from the process of intersocietal selection.  Differences that influenced societal growth and development have been especially important, because societies that have grown in size and developed in complexity and military power have been much more likely to survive and transmit their cultures and institutional patterns than societies that have preserved traditional social and cultural patterns and minimized innovations (1991, p. 63).