The political history of the world is the history of the various political entities created by the human race throughout their existence and the way these states define their borders. Throughout history, political systems have expanded from basic systems of self-governance and monarchy to the complex democratic and totalitarian systems that exist today. In parallel, political entities have expanded from vaguely defined frontier-type boundaries, to the national definite boundaries existing today. Prehistoric era The primate ancestors of human beings already had social and political skills. The first forms of human social organization were families living in band societies as hunter-gatherers. After the invention of agriculture around the same time (7,000-8,000 BCE) across various parts of the world, human societies started transitioning to tribal forms of organization. There is evidence of diplomacy between different tribes, but also of endemic warfare. This could have been caused by theft of livestock or crops, abduction of women, or resource and status competition. The Three-age system of periodization of prehistory was first introduced for Scandinavia by Christian Jürgensen Thomsen in the 1830s. By the 1860s, it was embraced as a useful division of the "earliest history of mankind" in general and began to be applied in Assyriology. The development of the now-conventional periodization in the archaeology of the Ancient Near East was developed in the 1920s to 1930s. Ancient history The early distribution of political power was determined by the availability of fresh water, fertile soil, and temperate climate of different locations. These were all necessary for the development of highly organized societies. The locations of these early societies were near, or benefiting from, the edges of tectonic plates. the Indus Valley Civilization was located next to the Himalayas (which were created by tectonic pressures) and the Indus and Ganges rivers, which deposit sediment from the mountains to produce fertile land. A similar dynamic existed in Mesopotamia, where the Tigris and Euphrates did the same with the Zagros Mountains. Ancient Egypt was helped by the Nile depositing sediments from the East African highlands of its origins, while the Yellow River and Yangtze acted in the same way for Ancient China. Eurasia was advantaged in the development of agriculture by the natural occurrence of domesticable wild grass species and the east-west orientation of the landmass, allowing for the easy spread of domesticated crops. A similar advantage was given to it by half of the world's large