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Southern Asia
Two billion people below the Himalayas, plus Iran
Southern Asia is the most densely peopled subregion on earth: about 2.08 billion residents, a quarter of humanity, packed into less than five percent of the world's land. The UN counts nine countries — India, Pakistan, Bangladesh, Nepal, Bhutan, Sri Lanka, the Maldives, Afghanistan, and Iran — and the last two are where the definition strains. Iran is culturally and politically Middle Eastern by any ordinary reckoning, and Afghanistan sits as plausibly in Central Asia. Strip them out and what remains is the Indian subcontinent, a landmass so distinct that it is a tectonic plate of its own, still driving north into Eurasia at about five centimeters a year.
That collision built the Himalayas, and the range walls the region off from the rest of Asia along a 2,400-kilometer arc that includes Everest, K2, and every one of the world's fourteen peaks above 8,000 meters. Their snowmelt feeds the Indus, the Ganges, and the Brahmaputra, whose combined alluvial plain is the most fertile and most crowded flat land anywhere. South of it the Deccan Plateau rises, dry and ancient, before the peninsula tapers to Kanyakumari. The southwest monsoon arrives in June and delivers most of the year's rain in a few months, and whether it comes early, late, or weak still determines how a billion people eat.
Indus Valley cities were laid out on grids while Egypt was still building pyramids, and the subcontinent has since produced Hinduism, Buddhism, Jainism, and Sikhism, and absorbed Islam so thoroughly that it now holds more Muslims than the Arab world. Two centuries of British rule ended in 1947 with a partition that displaced perhaps fifteen million people and killed a million more, and the India-Pakistan border has been armed and nuclear ever since. India is now the world's most populous country and among its fastest-growing large economies; Bangladesh has become a garment powerhouse; Afghanistan, under the Taliban again since 2021, is among the poorest places on earth.