Early civilization

The first Agricultural Revolution led to several major changes. It permitted far denser populations, which in time organised into states. There are several definitions for the term, "state." Max Weber and Norbert Elias defined a state as an organization of people that has a monopoly on the legitimate use of force in a particular geographic area.

Borders delineate states — a prominent example is the Great Wall of China, which stretches over 6,400 km, and was first erected in the 3rd century BCE to protect the north from nomadic invaders called Xiongnu. It has since been rebuilt and augmented several times.
The first states appeared in Mesopotamia, western Iran, ancient Egypt and Indus Valley in the late 4th and early 3rd millennia BCE.[citation needed] In Bronze Age Mesopotamia and Iran, there were several city-states. Ancient Egypt began as a state without cities, but soon developed them. States appeared in China in the late 3rd and early 2nd millennia BCE.
A state ordinarily needs an army for the legitimate exercise of force. An army needs a bureaucracy to maintain it. The only exception to this appears to have been the Indus Valley civilization, for which there is no evidence of the existence of a military force.
Major wars were waged among states in the Middle East. About 1275 BCE, the Hittites under Muwatalli II and the Egyptians under Ramesses II concluded the treaty of Kadesh, the world's oldest recorded peace treaty.[5]
Empires came into being, with conquered areas ruled by central tribes, as in the Neo-Assyrian Empire (10th century BCE), the Achaemenid Persian Empire (6th century BCE), the Mauryan Empire (4th century BCE), Qin and Han China (3rd century BCE), and the Roman Empire (1st century BCE).
Clashes among empires included those that took place in the 8th century, when the Islamic Caliphate of Arabia (ruling from Spain to Iran) and China's Tang dynasty (ruling from Xinjiang to Dalian) fought for decades for control of Central Asia.

Cuneiform script, the earliest known writing system.
The largest contiguous land empire in history was the 13th-century Mongolian Empire. By then, most people in Europe, Asia and North Africa belonged to states. There were states as well in Mexico and western South America. States controlled more and more of the world's territory and population; the last "empty" territories, with the exception of uninhabited Antarctica, would be divided up among states by the Berlin Conference (1884-1885).