When leaders of the Brics group of emerging economies meet in New Delhi on September 12-13, India will confront an awkward paradox: the grouping has never been bigger or harder to make coherent. What informally began as a four-member bloc comprising Brazil, Russia, India and China in 2006 has expanded into a grouping spanning Asia, Africa, the Middle East and Latin America. Its members include major energy exporters, manufacturing powers, emerging economies and countries with sharply different...