The people of the ancient world faced numerous challenges. They had to adapt to their environment first and foremost. Once they moved from a hunter-gatherer culture to a more sedentary civilization that relied on agriculture, ancient people had to learn how to sustain their populations. This usually entailed discovering how to irrigate their crops, domesticate their animals, and protect their supplies and resources from enemies and invaders.
The geography of the areas where ancient people settled played a critical role in their ultimate success or failure as a civilization. Those with natural defenses, abundant natural resources, ready access to water, and a mild climate thrived and expanded, whereas those lacking such essential features were easily overtaken. The earliest civilizations settled in river valleys: Mesopotamia, India, China, and Egypt. These civilizations persevered for centuries despite invasion and conflict, both internal and external. Other civilizations arose in different parts of the world, though none was more powerful or more widespread than the Roman Empire, which effectively controlled the entire Mediterranean.
The ancient world came to an end with the fall of the Roman Empire in 476 CE. The eastern half of what had been the Roman Empire went on to thrive as the Byzantine Empire, one of the strongest civilizations the world has ever known. During the first millennium CE, Asian cultures further developed and solidified their identities, and cultures in the Americas were heavily influenced by European explorers and conquerors.
The ancient and early-modern world was ultimately shaped by cultural diffusion, conflict, trade, and war—factors that continue to influence the development of the modern and post-modern world.