Sokoto Sultan and President-General of the Nigerian National Supreme Council for Islamic Affairs (NSCIA) Muhammad Sa'ad Abubakar stands during a meeting with US Secretary of State the Palace of the Sultan in Sokoto, on August 23, 2016. John Kerry congratulated Nigeria on its recent military successes against Boko Haram, but warned the country will face a blowback if it "cracks down" on the Islamists with excessive force. The top US diplomat, who was in Kenya on August 22, is expected to discuss the Boko Haram insurgency, fighting corruption and boosting Nigeria's moribund economy that has been pummelled by the drop in global oil prices. / AFP PHOTO / PIUS UTOMI EKPEIPIUS UTOMI EKPEI/AFP/Getty Images