Since the end of World War II and the birth of the modern global economy, business leaders have come to accept an iron law: International trade always expands faster than economic growth. Between the late 1940s and 2013, that assumption held true. Trade grew roughly twice as fast as the world economy annually, as fresh markets opened up, governments signed free-trade pacts, new industries and consumers emerged, and technological advances made international trade cheaper and faster. Now this iron law may be crumbling.