Each sample, referred to in our examination of typical civilizations, was built around a center, nucleus or homeland consisting of one or more cities with their adjacent hinterlands. The nucleus of the developing civilization was also the nucleus of an empire. Each nucleus was a center of planned production; accumulating wealth, growing population and expanding authority. Certain locations are better suited than others to provide the essentials of a civilization nucleus. The first requirement for a nucleus is a tolerable climate, primarily a satisfactory balance between heat and cold. Before the general use of fire as a source of warmth human populations were concentrated at or near the tropics. With the increasing use of artificial heating and lighting human beings were able to cluster farther and farther away from concentrated equatorial sunlight. The second requirement of such a location is a strategic position in a crossroads, in a network of transportation and communication. The third requirement is a readily available source of the food and building materials necessary to feed, house, and clothe a community and provide it with some of the niceties of daily living. The fourth requirement is the presence of sufficient man-power to operate the nucleus and provide a surplus for defense and for its extension and expansion. The fifth requirement is defensibility against aggression or invasion. The sixth essential is the availability of sufficient raw materials to meet the requirements of the nucleus, provide the exports needed to maintain a favorable trade balance for the nucleus and permit of its expansion, advancement and enrichment. Seventh, and in some ways, the most important requirement for the establishing of an empire or a civilization nucleus, is the presence of a will to live, a will to grow, a will to advance, competence in management, and a dogged persistence that will remain constant through generations or centuries of adversity, and still more demanding, through long periods of security, comfort and affluence. Eighth, and by no means least important, is the capacity to fight and win the aggressive trade and military wars incidental to the defense and expansion of the nucleus, of the empire, and eventually of the civilization. The ninth requirement is tolerance, receptivity to new ideas and practices, the capacity to adapt and to assimilate the outside elements which are constantly incorporated into the growing, expanding empire or the civilization. Finally, as we read the history and observe the development of nuclei, empires and civilizations, we are impressed by the role of outstanding individuals who occupy positions of responsibility over sufficiently long periods or with sufficient intensity to leave a lasting impression on the ideas, practices and institutions of their times. This requirement covers the practice of effective leadership.