The origin and development of armies and armed forces is connected with the formation and development of class society and the state. It is only with the formation of the first class society, which was the slave system, that the army appears. With the development of productive forces, with the change in industrial relations, the nature and methods of warfare changed, and with it the forms of organization of the army. The forms of organization of armies, genera and types of troops are usually adapted to the forms and methods of warfare. The militias and standing armies of the slave-owning period were replaced by recruiting and mercenary troops of the feudal era, and the latter gave way to cadre armies of the modern type, existing, with rare exceptions, on the basis of universal military service.