Greater numbers, or superior organization, might have given them an advantage, but we can hardly believe that the nomads were as numerous or had as good an organization as that of the people of the Pueblos. The region in which they presumably lived would certainly not support a large population, and particularly one with an essentially parasitic economy which did not produce. With such an economy, people cannot live too close together without exhausting the available resources, and a thinly spread population is unlikely to be highly organized. Great physical superiority may be another factor in the winning of battles between people who have not yet become so civilized as to have machines which will enable one individual to kill thousands of his fellow men. Any physical superiority, however, would seem to rest with the sedentary people who had an assured food supply. Moreover, their life was still sufficiently rugged so that there can hardly be any question of their having been greatly weakened by soft living. Doubtless, there were sporadic raids by nomads, and these may have had a cumulative effect in upsetting Pueblo economy. The role played by periods of arroyo-cutting and by droughts can certainly not be overlooked. These may well have done more than reduce the food supply. When food is scarce, raids are more likely to occur, and it is entirely probable that the relationship between various groups deteriorated as prosperity decreased. Toward the end of Great-Pueblo times we find increasing signs of warfare in the form of burned buildings and unburied bodies, many of which show evidence of violence. The latter are of the characteristic Pueblo type, however, and would seem to indicate warfare between people of the same blood. [Illustration: Fig. 28—Types of Great-Pueblo masonry. a. Chaco, b. Mesa Verde, c. Kayenta.] The most logical theory seems to be that many factors contributed to the great change which occurred in the Anasazi province. Doubtless, climatic conditions were the great underlying cause, but there may have been others. We cannot afford to confine our attention entirely to material causes, but must take into consideration even the possibility that fears, engendered by religious beliefs, may have played a part. All this, however, is largely in the realm of conjecture, for, with no written records, there can be no first hand information.