Port Harcourt, a sprawling "oil city" in the Niger Delta with more than 1.3 million residents, has seen a significant drop in oil production over the past two years due to a campaign of violence being conducted by militia and vigilante groups against the many multi-national companies doing business there. Gang violence there first became a major concern in 1999, when political candidates paid armed youths to help sway elections through intimidation and violence, an occurrence that was repeated during subsequent elections in 2003 and 2007. The Nigerian army continually raids gang and militia camps, but the groups are very widespread and have proved difficult to subdue. New gang members are paid more than most office workers in the city. These gangs for the most part claim that by asking for a share of Nigeria's oil wealth, they are fighting for the interests of the indigenous people of Rivers State and the Niger Delta region. The Movement for the Emancipation of the Niger Delta, or MEND, began a campaign of violence against foreign oil companies in early 2006 with the aim of driving the oil-refining corporations out of Port Harcourt. Until late last year, when a curfew was imposed, several armed gangs fought in the streets for control of the city. The curfew was lifted on New Year's Eve 2008, and the violence has returned, with MEND being a leader in attacks on foreigners. Also involved are the Niger Delta Vigilantes, a militant group with ties to MEND. Gunmen have conducted their campaign over the course of 2007 and 2008 through kidnappings of foreigners, ambushes against the Nigerian military (which tries to protect the refineries) and attacks on the refineries themselves. These gunmen have succeeded in shutting down 20 percent of Port Harcourt's oil production. More than 200 foreigners have been kidnapped by gunmen in the region in the last two years, although nearly all were released unharmed.