The Indus Valley civilization arose along the Indus River in modern-day Pakistan around 1900 BC and had large, well-planned cities with advanced sewer systems and indoor plumbing. By 1700 BC, the civilization declined for unknown reasons, possibly due to invasion by Aryans, changing weather patterns, or a combination of factors. Early Chinese civilization began along the Huang He and Yangtze Rivers in dynasties like the Xia, Shang, and Zhou. The concept of the Mandate of Heaven justified changes in ruling dynasties and rebellions based on a ruler's wisdom. Chinese society had a feudal system, social classes, ancestor worship, and advancements like writing, silk, coinage