Against a backdrop of growing calls for ethnically based separatism, including in former President Olusegun Obasanjo’s native Yorubaland, the former president in a speech laid out the arguments for maintaining Nigeria’s unity—though not at any cost. Speaking June 9 in the Yoruba heartland city of Abeokuta, where he lives in retirement, Obasanjo argued that Nigerians will fare better staying together: “it is better for Nigeria to remain as one indivisible nation than for each tribe to go its separate way.”

Trade between the world’s two biggest economies has ballooned in recent decades, bringing significant benefits but also perils that have led to calls to rethink the relationship.

Each Friday, I look at what the presidential contenders are saying about foreign policy. This Week: Donald Trump gave his most detailed interview on foreign policy yet. He made some dubious claims bu…