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  • NARRATOR: Humans civilizations have been wonderfully diverse

  • with an amazing variety of unique customs,

  • religious practices, social structures and technologies.

  • These differences are fascinating,

  • but Big History teaches us to look at the past differently,

  • to seek out commonalities and identify patterns

  • that unite seemingly unrelated phenomena.

  • Often this produces insights that are even more interesting.

  • One of the most important patterns we see

  • among agricultural civilizations is the need to expand.

  • Many agrarian civilizations grew to control

  • a lot of territory.

  • The Roman Empire at its peak controlled

  • around 2.5 million square miles,

  • the Persians more than three million square miles

  • and the Mongols a whopping 10 million square miles

  • with an empire stretching across Asia.

  • Though these empires existed in different places

  • and at different times, they shared a strong drive

  • to expand geographically.

  • And when they could no longer grow,

  • their territory shrank and eventually

  • their civilizations collapsed.

  • So why was geographic expansion so essential to their survival?

  • Maintaining a state was expensive.

  • Increasing the large populations required more infrastructure,

  • more resources as well as bigger governments and militaries.

  • Ambitious monumental architecture like the Pyramids

  • added even more expense because land productivity

  • had its limits and leaders could face rebellion

  • if they try to squeeze subjects too much

  • with heavy taxation.

  • There were limits to how much states could grow

  • using internal resources.

  • Thus growth necessitated taking what others had produced

  • rather than trying to increase productivity within the state.

  • During the era of agrarian civilizations

  • this type of military expansion was common.

  • We see it in civilizations around the world

  • with the Persians, the Romans, the Chinese dynasties

  • and with the Aztec and Inca empires in the Americas.

  • Large professional armies required food, weapons

  • and complex infrastructures like roads, forts

  • and defensive walls.

  • All of these came at great expense,

  • which itself increased the need for expansion.

  • Some military innovations lead to inventions

  • that would advance entire civilizations.

  • Iron is a good example.

  • The hard metal was initially used for weapons

  • but once iron plows appeared,

  • crop yields increased, and so did populations.

  • Roads, initially designed to move armies,

  • became important trade routes and building techniques

  • were refined after the construction of so many walls,

  • forts and watch towers.

  • Throughout this era, borders were constantly contested

  • but there was another side

  • to the interactions that took place.

  • Outposts and border regions often became centers

  • for commercial and technological innovation.

  • This was because different cultural groups

  • connected and many non-military exchanges occurred,

  • intensifying collective learning.

  • We see this accelerated change very clearly in Europe

  • when the Roman Empire splintered into a series

  • of small competitive states.

  • This increase in commerce and the exchange of ideas

  • drove a transition of power

  • from large agrarian civilizations

  • to these smaller commercial states.

  • The pace of collective learning further intensified.

  • Traditional agrarian civilizations in other parts

  • of the world lost power and in many cases were colonized

  • by the same European states with dramatic implications

  • for today's world.

  • Empires were shaped less by physical borders

  • and more by spheres of commercial influence.

  • The modern world had begun to take shape.

NARRATOR: Humans civilizations have been wonderfully diverse

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B2 AU expansion empire expand commercial military square

Why Did Civilizations Expand? | Big History Project

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