The Mekong River of mainland Southeast Asia provides water in six different countries for agriculture, trade and millions of people. But the Mekong region is in a severe drought, in part because of El Nino weather patterns. As stress on diminishing water resources increases, it will be difficult for Southeast Asia, already geographically and ethnically fractured, to foster cooperation. Yet the drought also carries opportunity for the overarching competitions in the region. Beijing is moving overland, expanding its economic trade routes and supply lines. The Mekong River is one aspect of this broader strategy. And amid a drought, China could use its influence over the control and release of water to gain concessions in other regional battles....