The Islamic State of Iraq and Levant – commonly known as ISIS – have become notorious as one of the most brutal extremist groups in the Syrian war. Recently, pictures circulated on the internet of two men who had been crucified by the group. Stories abound of beheadings, kidnappings, and worse. Originally an offshoot of Al-Qaeda, ISIS has since disassociated from the international terror network. But that has not hindered its progress.

Across the border in Iraq, the group has made its biggest victory yet: taking control of Mosul, Iraq’s second biggest city. With a population of 2 million, Mosul is on Iraq’s main oil export route. Troops and residents have fled, and the group has freed more than 1000 prisoners (some reports say as many as 2,400). It is a major setback for the Baghdad government’s fight against the fast growing insurgency – ISIS had already taken control of Ramadi and Falluja. The prime minister, Nouri al-Maliki, has called for a state of emergency to be declared. Other politicians are reluctant to grant Maliki these sweeping powers, afraid that he will not give them up once the crisis is over. During the last parliament, he centralised power, taking control of the security forces and allegedly influencing the courts.

Many in Iraq and abroad are asking: how has it come to this? ISIS has a total of 3-5000 fighters. The numbers that took Mosul were reportedly in their hundreds, although it is thought they had help from other militant forces. Armed only with rocket-propelled grenades and rifles, the group somehow prompted US-trained soldiers – with tanks – to abandon their posts and run. Of course, longstanding, ongoing sectarian tensions in Iraq have done nothing to help. The Iraqi government – dominated by Shias – has been engaged in a stand-off with the Sunni minority for months. Maliki has been heavy-handed in his treatment of Sunni protests about his perceived pro-Shia bias, citing concerns about terrorists in the midst of the protesters. This repression has, no doubt, played a role in worsening tension.

Before being ousted by the US, dictator Saddam Hussein did everything in his power to exacerbate and deepen sectarian divides between Iraq’s three main groups – Kurds, Sunnis, and Shias. These tensions bubble under the surface, problematising day to day governance and occasionally erupting into all out violence. In 2006-7, the country fought a bloody sectarian war. Violence has continued – as New Humanist reported last month, around 2000 people were killed in the first three months of this year. These tensions and divisions create clear space for terrorists to exploit. Some local Sunni tribes do not see the Mosul takeover as a militant occupation, but as another chapter in the sectarian struggle between Sunni and Shia. Therefore, even though they might not sympathise with the extreme views of ISIS, they support the group. It is for this reason that, on hearing the news of the ISIS takeover, many international commentators have instantly started talking about dividing Iraq into three distinct regions

Whether or not this happens remains to be seen, but ISIS now controls considerable territory in eastern Syria and western and central Iraq. This shows considerable progress in its aim of setting up a “Caliphate State” that straddles the border. Clearly, the long chapter of violence and unrest in Iraq is far from over.