The devastating oil spill in the Gulf of Mexico has led us to consider the effects of oil contamination in other parts of the world. Nigeria's oil-rich Niger Delta is considered to be the world capital of oil pollution. But it's a violent place – armed gangs attack people who work for the oil industry, kidnapping workers and blowing up pipelines – and the area is under the control of the Nigerian military.

Secretary of State Hillary Clinton continues her eleven-day tour of the African continent. After introducing a monetary commitment to Congo to help prevent sexual violence, the next country on her agenda is Nigeria. The oil rich nation is plagued by violence and corruption and President Obama skipped the nation on his last trip to Africa. Secretary Clinton is expected to have strong words for the country and to continue the push for a 60-day amnesty period on violence in the Niger Delta, which was declared in hopes to end years of militant attacks that have hobbled the oil industry there. BBC Correspondent Caroline Duffield is covering the Secretary of State's travels in Africa.