On Feb. 24 the United Nations Development Program commemorated its 50th anniversary. Beneath the boisterous celebration of past achievements, a UNDP background paper quietly sounded a sobering note. “Significant deprivations persist,” the paper stated, “and many problems faced today are deep-seated, structural in nature, and not susceptible to quick fixes.”

Such caution was in scarce supply in the heady early days of the U.N. after World War II, when wealthy nations poured money into the Third World in the belief that poverty...