The civilization that began along China's river systems 3,500 years ago continues today due to China's relative geographic isolation. China's geography, with natural barriers like long rivers and mountain ranges occupying much of its land, isolated early Chinese settlers who had to become self-sufficient rather than trade. Throughout China's history, dynasties like the Shang, Zhou, Qin, and Han expanded its political boundaries and centralized government while Chinese culture remained the dominant influence. Confucianism became the dominant ideology and family was the central social institution in Chinese society.