The Indus Valley Civilization was one of the earliest civilizations in South Asia, contemporary to Mesopotamia and Ancient Egypt. It peaked around 2500 BCE along the Indus River valley in modern-day Pakistan and parts of India. The civilization was highly advanced and urbanized, with many large cities. However, it declined around 1900 BCE, possibly due to changes in the monsoon patterns. The writing system of the Indus Valley Civilization remains undeciphered. The author proposes a theory that the civilization was destroyed by invading Pre-Dravidian groups from South India, and its people migrated and mixed with the local Pre-Dravidian population, eventually developing into the Dravidian culture.