The largest terrorist group based out of northeastern Nigeria is called Boko Haram. This Islamic extremist group has terrorized the nation and a few surrounding countries since 2002. The main idea of the group is to oppose westernization. On April 14, 2014, they kidnapped 276 students from a girls' secondary school in Chibok, Nigeria. Only a few have been returned, and an outcry erupted from the nation and the world, begging for justice. The girls who attended that school were some of the most aspiring people in their community, which is likely why Boko Haram decided to take them and show the world how they deal with what they despise.
Although Nigeria is the largest producer of oil in Africa, it doesn't have enough to satisfy the demands from its market. The companies that Nigeria imports oil from to meet its national needs recently have decreased the amount they send because of their own shortages, which hurts Nigeria. Also, the country only has 4 oil refineries, which causes them to produce their oil slowly. Nigeria's economy rests mainly on oil sales, so if this decently unstable industry were to collapse, their whole economy could fall apart, hence the term "crisis."
Throughout the region, they deal with a problem the rest of the world is also familiar with: Christianity vs. Islam. The tensions and violence have been present since 1953. Currently, Sharia law is practiced in some parts of or all of 12 Nigerian states, which upsets many Christians in the country. The northernmost piece of the country is under Sharia law, the southernmost piece is predominately Christian, and the middle belt is mixed. Many religious and cultural differences and violent attacks against each other keep the two groups from living together peacefully.
Oil brings money, and money makes the world go 'round. Who doesn't want a big stack of cash from selling something you can easily force others to drill up out of the ground for your own benefit? Different minority groups have a grand old time getting forced by more powerful people and large companies to do the hard work so the bullies can have the money to themselves. If you want to turn out on top, round up a gang of like-minded people and become a small militia to get your oil through acts of violence, such as kidnapping and piracy :). The delta has also been dominated by multiple oil spills, mainly from Shell, that damage the fish population (including 20 species found nowhere else in the world), surrounding farms, and nearby forests.