Nigerian troops battled militia forces Thursday in the creeks and mangrove swamps of Africa’s leading oil region, the Niger Delta, pressing an offensive that has forced thousands of villagers to flee their homes for this petroleum hub. Burned houses and twisted corrugated iron roofs — strewn flat over an area of a football field — bore witness Thursday to the savagery of militia attacks on one slum district in Port Harcourt, a city of 3 million and Nigeria’s most important oil center. Full Story