A theory of demographic cycles is developed by the author out of the contributions of many sciences. F. Braudel named these cycles as "secular trends," and R. Cameron used the concept of "logistics cycles." The author constructs a mathematical model of a demographic cycle. With the help of this model the cycle is divided into phases for which the author is able to determine about 40 qualitative attributes of the cycle. These attributes allow a demographic cycle to be identified in the real course of a history even in the absence of quantitative data about a population. With the help of this method 57 demographic cycles are identified in the history of the various countries of the East. In particular, it is shown that the increase of demographic pressure at the end of a cycle results in establishment of étatist monarchy.