For decades, early twentieth-century historians attributed the rapid collapse of the Bronze Age Indus Valley Civilization around 1900 BCE to violent foreign military invasions. However, modern archaeological excavations and paleoclimatic data have comprehensively debunked this catastrophic invasion hypothesis. Oxygen-isotope analysis of stalagmites in Himalayan caves and sediment cores from Arabian sea basins reveal a progressive weakening of the Indian summer monsoon lasting several centuries. As seasonal monsoon rains retreated eastward, the once-mighty Ghaggar-Hakra river system desiccated into seasonal streams. Deprived of reliable irrigation for agricultural surpluses, residents were unable to sustain urban hubs like Harappa and Mohenjo-daro, prompting a gradual de-urbanization and eastward migration toward smaller agrarian settlements along the fertile Ganges basin.