In 1969, Phillips Petroleum was poised to abandon exploration of the Norwegian continental shelf when the company decided to drill one last oil well — and hit the jackpot. The discovery made Norway one of the world’s richest countries. Its sovereign wealth fund, established to invest the money, now manages about $2 trillion, equivalent to roughly $340,000 for every Norwegian.For years, oil revenue and the wealth fund have helped this tiny nation to enjoy low unemployment, low government debt and...