At the end of the 2nd millennium BC, a form of Chinese was spoken in a compact area around the lower Wei River and middle Yellow River. From there it expanded eastwards across the North China Plain to Shandong and then south into the valley of the Yangtze River and beyond to the hills of south China. As the language spread, it replaced formerly dominant languages in those areas, and regional differences grew. Simultaneously, especially in periods of political unity, there was a tendency to promote a central standard to facilitate communication between people from different regions.