Complex sentence: This civilisation collapsed at the start of the second millennium BCE and was later followed by the Iron Age Vedic Civilisation; the era saw the composition of the Vedas, oldest scriptures associated with Hinduism; and social stratification emerged based on caste.
Split into simpler sentences: This civilisation collapsed at the start of the second millennium BCE and was later followed by the Iron Age Vedic Civilisation. The era saw the composition of the Vedas, the seminal texts of Hinduism, and social stratification based on caste.