Memo Question for May 7: Divergence, Bigtime

May 7: The economic history of the world both in the post-WWII period 1945-1990 and, in broader perspective, over the past two centuries has been one in which the world has shrunken enormously in distance along every conceivable measurement, and yet in which income and productivity differences between societies have grown enormously. What, in your judgment, are the possible big-picture theories for explaining this phenomenon that are worth investigating?