Secretary of State John Kerry said Friday that “an era of American diplomatic engagement” is following a decade defined by force. One day after Iran’s president took the stage here seeking to assure the world that his country did not aspire to develop nuclear weapons, Secretary of State John Kerry pushed back on Friday, challenging him to demonstrate that the Iranian nuclear program was peaceful. “He told you that Iran has no intention of building a nuclear weapon,” Mr. Kerry said in a speech to the World Economic Forum. “Starting now, Iran has the opportunity to prove these words beyond all doubt to the world.” Mr. Kerry laid down several requirements for the comprehensive nuclear agreement that Iran and six world powers are now preparing to negotiate, saying that Tehran must accept extensive verification, abandon plans to build a heavy-water reactor […]