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Indus Valley Civilization
One of the first true great ancient civilizations, the Indus included parts of modern-day India, Pakistan, Iran and Afghanistan. Famous for its walkways, high buildings, and metallurgy shops, the civilization’s population at its peak reached 5 million, which amounted to around 10% of the world’s entire population at the time. The people vanished 3,000 years ago, most likely as a result of changes in rainfall that made it difficult to grow enough food to sustain the huge population.
