ONITSHA, Nigeria -- The legend of Cardinal Francis Arinze, a contender to become the first pope from Africa in 1,500 years, stems from a moment of crisis in Nigeria's Catholic heartland. It was the early 1970s, and the government had ordered all European and American priests -- most of the Catholic leadership at the time -- out of the country. The political purge left Arinze and a handful of Nigerian priests with a massive job and few resources to do it, church leaders here said. But Arinze, the first African-born archbishop in this grubby trading center on the Niger River,...