The violence that occurred Sunday was primarily Muslim against Christian, which was a retaliation to Christian attacks that happened back in January.
From this Associated Press article that we found at The Guardian, writer Jon Gambrell gives us this explanation.
Sunday's bloodshed was mostly about revenge: Christian villages near the city of Jos were attacked before dawn, less than two months after Muslims were targeted and a mosque torched. Hundreds had been killed in January, their corpses stuffed into wells and sewage pits.
Survivors of the weekend attack say simple, one-room houses were set ablaze, the flames illuminating villages that have no electricity. Residents, mostly of the minority Berom ethnic group, ran from their burning homes. Assailants with machetes were waiting. Many of those who were cut down were children. At least 200 people died.
One 20-year-old man arrested for allegedly taking part in Sunday's attacks said his family members died at the hands of rioters in January. Of those who were attacked on Sunday, he said: "There are some people that kill all our parents. We went to avenge what they did to us."
Nigeria, a nation of 150 million people, is almost evenly split between Sunni Muslims in the north and the predominantly Christian south. The recent bloodshed has been happening in central Nigeria, where dozens of ethnic groups vie for control of the nation's fertile "middle belt."
"Jos is a mini-Nigeria. All segments of Nigeria are here," said state police commissioner Ikechukwu Aduba.
After the January violence, human rights groups said text messages had been sent with the addresses of mosques and churches. Texts also offered instructions on how to dispose of bodies. One read: "Kill them before they kill you."
Survivors said the weekend attackers asked people "Who are you?" in Fulani, a language used mostly by Muslims, and killed those who did not answer back in Fulani.
Aduba, though, said some attackers had been paid by organizers to commit the killings Sunday, but he declined to give any specifics.