How did India and China, nuclear-armed nations collectively home to 36 percent of the world’s people, go from conflict to camaraderie in less than a week? At the end of August, two months into the worst border standoff between the two countries in decades, there were whispers of war. But this week, Indian Prime Minister Narendra Modi and Chinese President Xi Jinping joined Russia, South Africa and Brazil in declaring war on Pakistan-based terror groups. What just happened? Can it last? And should we trust it? For the moment, it appears Beijing’s aspirations to be a global leader in a...