Like the robber barons of the 19th century Gilded Age, a new and proliferating crop of billionaires is driving rapid development and industrialization in poor countries. The accelerated industrial growth spurs economic prosperity for some, but it also widens the gap between the super rich and the rest of the population, especially the very poor.

In Rich People Poor Countries, Caroline Freund identifies and analyzes nearly 700 emerging-market billionaires whose net worth adds up to more than $2 trillion. Freund finds that these titans of industry are propelling poor countries out of...