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
Solar power plants in the Mojave Desert also plans to build other large solar plants in the Mojave Desert. The southwestern United States is one of the world's best areas for insolation, and the Mojave Desert receives up to twice the sunlight received in other regions of the country. This abundance of solar energy makes solar power plants a cleaner alternative to traditional power plants, which burn fossil fuels such as oil and coal. Solar power stations provide an environmentally benign source of energy, produce virtually no emissions, and consume no fuel other than sunlight. Some groups are also encouraging more distributed generation, or rooftop solar. In