The Indian Subcontinent

The Indian subcontinent is a fragment of the old supercontinent Gondwana that broke away, crossed an ocean, and crashed into Asia, and it still behaves like a separate continent that happens to be attached. The Himalayas, the Karakoram, and the Hindu Kush fence it off to the north, and the sea takes it on the other three sides. India, Pakistan, Bangladesh, Nepal, Bhutan, and Sri Lanka are always counted, the Maldives usually. Afghanistan is the argument: it sits on the Eurasian side of the geological suture, but its history pulls it both ways, and sources put it in or out at will. The UN prefers South Asia, partly so that India's name does not do all the work.

The collision is still under way, at about five centimeters a year, and it raised the highest mountains on the planet, Everest among them at 8,849 meters, along with the deep trough in front of them that the Indus, the Ganges, and the Brahmaputra have filled with sediment kilometers thick. That trough is the Indo-Gangetic Plain, some of the most fertile and most crowded farmland anywhere. South of it lies the older, harder Deccan Plateau, flanked by the Western and Eastern Ghats. The monsoon governs everything: about three-quarters of the year's rain falls between June and September, and the whole agricultural and economic calendar bends toward its arrival.

About 1.95 billion people, close to a quarter of humanity, live on land roughly the size of the European Union, which makes this the most densely peopled large region in the world. Hinduism, Buddhism, Jainism, and Sikhism all began here, and the subcontinent holds the largest Muslim population of any comparable region on earth. The Indus Valley civilization laid out planned brick cities more than 4,000 years ago. British rule and the 1947 partition into India and Pakistan, which uprooted perhaps 15 million people and killed a million, drew borders that remain among the most militarized anywhere. India is now the most populous country on earth; Bangladesh sits on the front line of sea-level rise.