While the cities of a particular region may have begun as self-governing political units, over time these city-states were brought together into a single political unit, usually by force. These larger political units are known as empires. The earliest empires were centered on river valleys where intensified agriculture had developed.
- 2340 BC: Sargon Akkad takes Sumer, establishing the first empire.
- c. 2125-2027 BC: The Third Dynasty of Ur
- 1900-1600 BC: The First Babylonian Empire
- c. 1900 BC: Ammorites establish Babylon
- 1792-1750 BC: Reign of Hammurabi
- c. 1600 BC: Invasions by Hittites and Kassites destroys the empire
- 3100-2686 BC: Archaic Period
- 2686-2181 BC: Old Kingdom
- 1991-1636 BC: Middle Kingdom
- 1578-1085 BC: New Kingdom
- 1085-332 BC: Late Dynastic Period
- 332 BC: Alexander the Great conquers Egypt
- 2600-2500 BC: Harappan Civilization is at its height
- 2000-1900 BC: Harappan Civilization collapses
- c. 1300 BC: Aryans migrate into the Indus Valley
- c. 1000 BC: Aryan migrate into the Ganges Valley
- 221-207 BC: Qin dynasty.
- 206 BC- AD 9: Former Han dynasty
- AD 25--220: Later Han dynasty
- 2000 BC-AD 925: Mayan Culture
- 2000 BC: Beginnings of Mayan culture
- AD 325-925: Mayan culture at its peak
- 600-800: Huari and Tiahuanaco empires
- 1438-1538: Inca Empire.
- c. 500 BC: Nok culture
- c. 500-450 BC: Development of iron smelting
- 500 BC - AD 500: The Bantu migrations
- 200 BC: Jenne-jeno founded
- AD 400: Height of the Niger River city-states