Early civilizations emerged during the Neolithic Revolution, transitioning from hunter-gatherer societies to settled agricultural communities. This period saw the rise of complex societies in Mesopotamia, Egypt, the Indus Valley, and China, each developing unique cultural and technological innovations. The classical period witnessed the growth of empires and major philosophical traditions. Greek city-states and the Roman Republic expanded their territories, while civilizations in Mesoamerica and the Andes developed advanced systems of astronomy, mathematics, and agriculture.