From the pier at Mundra, the biggest private port in India, it is possible, on a clear day, to spot the world’s largest oil refinery, 50km south across the Gulf of Kutch. In the early 1990s both sites in the state of Gujarat were malarial swamps and farmland. Today they are monuments to India’s economic promise—and to the tycoons who built them. Gautam Adani and Mukesh Ambani, both billionaires, have in recent years become the…