How did India and Bangladesh erase 200 islands of foreign territory in one day?

By swapping them all at once. Until 2015, the India-Bangladesh border held one of the strangest territorial tangles on Earth: more than 100 small pockets of India sitting inside Bangladesh, and over 50 pockets of Bangladesh sitting inside India, some of them nested inside each other like Russian dolls. Residents of these pieces of land, called enclaves, complained of being effectively stateless. On 1 August 2015, the two governments implemented a Land Boundary Agreement that exchanged 162 of these enclaves, 111 Indian and 51 Bangladeshi. Because some enclaves sat inside others, the swap also removed about two dozen second-order enclaves and one third-order enclave: 197 scraps of foreign territory erased on a single day, leaving only Bangladesh's Dahagram-Angarpota.

This wasn't a new kind of problem. The word 'enclave' is French, first used in the 15th century as a property-law term for a plot of land surrounded by someone else's land, so cut off that the law granted its owner a right of passage just to reach it. The same thing happened at the scale of nations: in feudal Europe, territories were bought, sold, inherited, and partitioned so many times that before 1866, Prussia alone was scattered across more than 270 separate pieces of land. An enclave is a territory surrounded entirely by one other country, like Lesotho, which sits completely inside South Africa, one of only three independent countries in the world in that situation. An exclave, a related but different idea, is simply a piece of a country separated from its main territory, whether or not it's technically surrounded by just one neighbor.

Not every country rushes to get rid of these oddities, though. Living in an enclave has often meant trouble with passage rights, importing goods, currency, utilities, health services and cooperation from the surrounding country, which is why enclaves have tended to be eliminated over time. But the Netherlands and Belgium decided to keep their enclave system in Baarle: as members of the European Union and the Schengen Area, people, goods and services flow freely there anyway.