Answer: The location of oases has been of critical importance for trade and transportation routes in desert areas; caravans must travel via oases so that supplies of water and food can be replenished. Thus, political or military control of an oasis has in many cases meant control of trade on a particular route. For example, the oases of Awjila, Ghadames and Kufra, situated in modern-day Libya, have at various times been vital to both north–south and east–west trade in the Sahara Desert. The Silk Road across Central Asia also incorporated several oases.
In North American history, oases have been less prominent since the desert regions are smaller, however several areas in the deep southwestern United States have oases regions that served as important links through the hot deserts and vast rural areas. While present day desert cities like Las Vegas, Phoenix, Palm Springs, and Tucson are large modern cities, many of these locations were once small, isolated farming areas that travelers through the western desert stopped for food and supplies. Even today, there are several roads that go through western deserts like U.S. Route 50 through southern Nevada, and the Mojave Desert that feature small green fields, citrus groves and small isolated supply towns.