Eighteen people, including two priests, were killed in an attack on a church in Makurdi, the capital of Benue State, on Tuesday. The killings were blamed on herdsmen and in retaliation 11 ethnic Hausa were killed and two mosques were attacked.

Nigeria's upper and lower houses of parliament have now called for President Muhammadu Buhari to appear before them over the continuing clashes between herdsmen and farmers and explain what the government has been doing to stop the violence. The lawmakers also called for the replacement of Nigeria's security chiefs. Yakubu Dogara, speaker of the lower house of parliament, tweeted that the parliamentarians could not look on as citizens were being killed.

An ECOWAS summit in Nigeria's capital Abuja on Thursday brought West African leaders together to address the issue. "We are aware of the recent escalation of the conflicts between herders and farmers, but there is no doubt that such conflicts are a common phenomenon in most parts of Africa," said Nigerian Interior Minister Abdulrahman Dambazau as he addressed the summit. ECOWAS members acknowledged that the problem was regional as nomadic groups often cross regional borders. They said there was a need for greater investment in livestock management, the livelihood of the herders, and that they had drafted a common agricultural policy.

Around 400 people have died in the clashes since the start of the year, according to a report by the US-based Armed Conflict Location and Event Data Project (ACLED). But the conflict is not new. According to the International Crisis Group, 2,500 people died in 2016. Around 175,000 have fled their homes and live as displaced persons within the country. Government critics say that Buhari and his administration have not done enough address the issue.

Perpetrators go unpunished

Nomadic cattle breeders need water and grass for their livestock so they send them to graze on local farmland. But that angers farmers who are using the land, and the scarce resources at their disposal, to grow crops. In recent months, a growing number of herdsmen and farmers have taken up arms and formed militias and the conflict has spread.

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"People are taking the law into their own hands," says Osai Ojigho, director for Amnesty International in Nigeria. The conflict tension has spread to as many as 17 states in Nigeria, but Benue is the state that is most affected. "Over time, populations have expanded around the areas where the nomadic communities have often moved their cattle across the country. And this goes beyond Nigeria, across the entire Sahel and West African region," says Ojigho.

The biggest problem, says human rights activist Sarli Sardou Nana, is that the perpetrators are not punished. "If nobody is being arrested, if nobody is being persecuted, then what people think is: I have to defend myself," he told DW.

Land, ethnicity, religion and politics

The state of Benue lies in central Nigeria. It's a place where the predominantly Muslim north and the Christian south meet. The recent attack on the church was, however, different to previous ones, which tend to escalate around land issues. "The pattern of Tuesday's attack was different from prior attacks," Cheta Nwanze of SBM Intelligence told news agency AFP. "So, to my mind at least, someone is taking advantage of the problem."

The conflict has changed, Nana agrees. "This conflict was initially a conflict over natural resources between farmers and herders, so people were competing over land. But gradually it was politicized and there are also religious manipulations that have been brought into the conflict. There are also criminal elements that have been involved. So there are hired killers for example," he said.

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With his NGO Stop Genocide Action Group, Nana is trying to address some of these issues. "When you kill a three-day-old child, that child is neither a farmer or a herder. You're killing the child because of their ethnic or religious background. That is genocide," he said.

Earlier this week Laolu Akande, a media assistant to Nigeria's Vice President Yemi Osinbajo, wrote on Twitter that he believed that whoever was behind the conflict was apparently trying to stir up a religious conflict.

Can 'cattle colonies' help?

Speaking to DW, Benue State's governor, Samuel Ortom agreed that the central government has to do more. "The federal government has the prerogative of enforcing the laws of the land. I don't have state police. I don't have a state army, I don't have the navy and airforce and all that," the governor said. President Buhari, on the other hand, has said that his government is doing everything in its power to maintain peace and security.

Last year the state of Benue passed a law banning pastoralists from moving around on its territory. But the attacks and retaliatory attacks are have not stopped.

One suggestion that often comes up is the concept of "cattle colonies" or designated grazing areas for pastoralists. That would mean that they could no longer continue their nomadic way of life. Ortom, however, does not believe that this can work: "Where will you get the land?" he asks. "In the 1950s, when cattle routes were designated and grazing areas were carved, the total population of Nigeria was less than 40 million people. Today we are approximated to be over 200 million."

Auwal Ibrahim Musa from Transparency International in Nigeria thinks that the cattle colonies can't be implemented on a large scale. "The only solution is that people talk to each other," he says. The reason these conflicts have escalated is, on the one hand, a lack of leadership from the side of the government and also the rising poverty and unemployment in the area. "Young people from both sides are victims of the state. They have no jobs, they have no proper orientation or understanding on how to live amicably or in harmony with one another," Musa says.

Nigeria is not the only country affected by such communal tensions. Similar clashes have occurred have cropped up in Mali, Ghana and Niger.

Adrian Kriesch, Jane Nyingi, Uwaisu Idris and Stefan Ehlert contributed to this report.