The current conflict in the Niger Delta first arose in the early 1990s over tensions between foreign oil corporations and a number of the Niger Delta's minority ethnic groups who feel they are being exploited, particularly the Ogoni and the Ijaw. Ethnic and political unrest continued throughout the 1990s despite the return to democracy and the election of the Obasanjo government in 1999. Struggle for oil wealth and environmental harm over its impacts has fueled violence between ethnic groups, causing the militarization of nearly the entire region by ethnic militia groups, Nigerian military and police forces, notably the Nigerian Mobile Police. The violence has contributed to Nigeria's ongoing energy supply crisis by discouraging foreign investment in new power generation plants in the region. From 2004 on, violence also hit the oil industry with piracy and kidnappings. In 2009, a presidential amnesty program accompanied with support and training of ex-militants proved to be a success. Thus until 2011, victims of crimes were fearful of seeking justice for crimes committed against them because of a failure to prosecute those responsible for human rights abuses. Environmental issues in the Niger DeltaPetroleum industry in NigeriaNigerian energy supply crisis and South South Nigeria, after nearly four decades of oil production, had by the early 1980s become almost completely economically dependent on petroleum extraction, which at the time generated 25% of its GDP. This portion has since risen to 60%, as of 2008. Despite the vast wealth created by petroleum, the benefits have been slow to trickle down to the majority of the population, who since the 1960s have increasingly been forced to abandon their traditional agricultural practices. Annual production of both cash and food crops dropped significantly in the later decades of the 20th century. Cocoa production dropped by 43% for example; Nigeria was the world's largest cocoa exporter in 1960. Rubber production dropped by 29%, cotton by 65%, and groundnuts by 64%.