Now most of the great mountain systems existences were developed moderately late in geological system. These are some greatest mountains are in North and South America they are the Andes, Rockies, Sierra Nevada, and Coast Ranges of the United States, Canada, and Alaska and the Eurasian mountain belt, in which lie the Pyrenees, Atlas, Alps, Balkans, Caucasus. And notable single peaks are Everest, K2(Godwin-Austen), and Kanchenjunga in Asia; Aconcagua, Chimborazo, and Cotopaxi in South America; McKinley, Logan, and Popocatepetl in North America; Mont Blanc and Elbrus in Europe; Kilimanjaro, Kenya, and Ruwenzori in Africa. Mountains are very important because it effects upon the climate, population, economy, and state of civilization of the regions in which they occur. By intercepting existing winds they cause precipitation; regions on the windward side of a great range thus have plentiful rainfall. Mountains are in general thinly populated, not only because the cold climate and rarefied atmosphere of high regions are unfavorable to human life, but also because the higher reaches of mountains are unfit for agriculture. Now many mountains have the valuable mineral ores, deposited out of solution by water or by gases and it acts as natural barriers between countries and people and they determine the routes followed by traders, migrants, and invading armies. The difficulties of travel and communication in mountain regions tend to favor political disunity.