Abstract: Through webs of cross-cutting ties, groups can build "social capital" -- the ability to use the resulting access to information and collective punishment to enforce on each other their norms of appropriate behavior. Yet not all minorities maintain such networks. And groups without them sometimes find themselves manipulated by opportunistic entrepreneurs who capture private benefits for themselves while generating massive hostility and (statistical) discrimination against the group as a whole. As one adage puts it, sometimes the worst enemy of a minority group is its own leadership. Consider the Korean residents of Japan. Koreans had begun to migrate to Japan in the 1910s. They were poor, single, male, young, uneducated, and did not intend to stay long. As one might expect given those characteristics, they maintained only very low levels of social capital, and generated substantial (statistical) discrimination against themselves. After the Second World War, most Koreans returned to their homeland. Among those who stayed, however, a self-appointed core of fringe-left opportunists took control and manipulated the group toward their private political ends. Lacking the dense networks that would let them constrain the opportunists, the resident Koreans could not stop them. Those with the most talent, sophistication, and education simply left the group and migrated into Japanese society. The opportunistic leaders exploited the vulnerable Koreans who remained, captured private benefits for themselves, and generated enormous hostility and (statistical) discrimination against the rest.