Enlarge / The Cambodian city of Angkor was once the largest in the world until vast swathes of the population decamped in the 15th century. Its famous temple, Angkor Wat (above), survived. (credit: Stefan Irvine/LightRocket/Getty Images)

The Cambodian city of Angkor was once the largest in the world… then the vast majority of its inhabitants suddenly decamped in the 15th century to a region near the modern city of Phnom Penh. Historians have put forth several theories about why this mass exodus occurred. A new paper in Science Advances argues that one major contributing factor was an overloaded water distribution system, exacerbated by extreme swings in the climate.

Angkor dates back to around 802 CE. Its vast network of canals, moats, embankments, and reservoirs developed over the next 600 years, helping distribute vital water resources for such uses as irrigation and to help control occasional flooding. By the end of the 11th century, the system bore all the features of a complex network, with thousands of interconnected individual components heavily dependent on each other.

Such a configuration, hovering at or near the so-called critical point, is ideal for the effective flow of resources, whether we’re talking about water, electricity (power grids), traffic, the spread of disease, or information (the stock market and the Internet). The tradeoff is that it can become much more sensitive to even tiny perturbations—so much so that a small outage in one part of the network can trigger a sudden network-wide cascading failure.