The Indus Valley civilization, one of the largest and most populous ancient civilizations, potentially fell due in part to climate change.
The Indus civilization developed 5,600 years ago and, at its peak, is believed to have held 10% of the world's population in the culture that expanded over 386,000 square miles, more extensive than ancient Egypt and Mesopotamia.
About a century ago, archeologists began finding evidence of old cities. Evidence suggests the cities were developed with grids and evidence of advanced plumbing, not seen again until Ancient Rome. Most notably, there was a startling lack of large buildings for royalty, which was typical of civilizations at the time.
With a civilization so populous, the mystery of why so many cities and buildings were abandoned seemingly overnight has gone unsolved for decades.
By reconstructing the landscapes of plains and rivers where these ancient civilizations once settled by analyzing satellite images of the area and collecting sediment samples.
Through these methods, the research teams could determine what crops were planted and when, how landscapes changed, and how that affected settlements.
Many of these cities were built on rivers fed by monsoon rains. As the climate changed and the monsoons became less frequent, crops and water sources were less reliable, facilitating a move east towards a reliable water source.
This shift devastated the Indus Civilizations, which relied on significant surplus years. As a result, larger cities collapsed as more minor, localized communities and economies started performing better.