History of the Great Wall of China the three, China's chief concern since the earliest times had been Mongolia – the home of many of the country's fiercest enemies including the Xiongnu, the Xianbei, the Khitans, and the Mongols. The Gobi Desert, which accounts for two-thirds of Mongolia's area, divided the main northern and southern grazing lands and pushed the pastoral nomads to the fringes of the steppe. On the southern side (Inner Mongolia), this pressure brought the nomads into contact with China. For the most part, barring intermittent passes and valleys (the major one being the corridor through Zhangjiakou and the Juyong Pass), the North China
Environmental issues in China the country. Approximately 30% of China's surface area is desert. China's rapid industrialization could cause this area to drastically increase. The Gobi Desert in the north currently expands by about per year. The vast plains in northern China used to be regularly flooded by the Yellow River. However, overgrazing and the expansion of agricultural land could cause this area to increase. In 2009, it was estimated that over 200 high-altitude lakes in Zoigê Marsh, which provides 30% of the Yellow River's water, had dried up. In 2001, China initiated a "Green Wall of China" project. It is a project to