A US-backed alliance of Syrian Kurdish and Arab fighters is closing in on the last pocket of territory in eastern Syria controlled by the jihadist group Islamic State (IS).
Four years ago, IS militants overran large swathes of Syria and neighbouring Iraq, proclaimed the creation of a “caliphate”, and imposed their brutal rule on almost eight million people. Now, they control only about 1% of the territory they once had.
However, the US military has warned that while the jihadists are “in the final throes of their evil ambitions” they are “not yet defeated“.
Between 1,500 and 2,000 militants are estimated to be holed up inside the area around the Syrian town of Hajin, in the Middle Euphrates River Valley, where the US says it has witnessed some of the most intense fighting in more than a year.
How IS lost its caliphate
The military campaign to push IS out of Iraq and Syria has been bloody, with thousands of lives lost and millions of people forced to flee their homes.
In Syria, troops loyal to President Bashar al-Assad have battled the jihadist group with the help of Russian air strikes and Iran-backed militiamen. A US-led multinational coalition has meanwhile supported the Kurdish-dominated Syrian Democratic Forces (SDF) alliance and some rebel factions.
In Iraq, security forces have been backed by both the US-led coalition and a paramilitary force dominated by Iran-backed militias, the Popular Mobilisation.
The US-led coalition, which included forces from Australia, Bahrain, France, Jordan, the Netherlands, Saudi Arabia, Turkey, United Arab Emirates and the UK, began launching air strikes against IS targets in Iraq in August 2014. The coalition’s Syrian air campaign began a month later.
Since then aircraft deployed as part of the coalition’s Operation Inherent Resolve have carried out more than 13,400 air strikes in Iraq and more than 16,100 in Syria.
Russia is not part of the coalition, but its jets began air strikes against what it called “terrorists” in Syria in September 2015 to bolster the government of President Assad.
The Russian defence ministry reported in August 2018 that its forces had flown 39,000 sorties in Syria since 2015, destroying 121,000 “terrorist targets” and killing more than 5,200 members of IS.
Key cities were recaptured
Early progress in the US-led coalition’s campaign against IS included the recapture of the city of Ramadi, the capital of Anbar province in Iraq, by Iraqi pro-government forces in December 2015.
The recapture of Iraq’s second city of Mosul in July 2017 was seen as a major breakthrough for the coalition, but the 10-month battle left thousands of civilians dead and saw more than 800,000 others forced to flee their homes in the city.
In October 2017, the city of Raqqa, so-called capital of the self-styled “caliphate”, was re-taken by the SDF with coalition air support, ending three years of rule in the city by IS.
After four months of fighting, thousands of IS soldiers were allowed to leave the city under a deal arranged locally with Syrian officials, but with the knowledge of the Syrian Democratic Forces, an alliance of Kurdish and Arab fighters and the US-led coalition.
The following month, the Syrian army regained full control of the eastern city of Deir al-Zour, and Iraqi forces retook the key border town of al-Qaim.
Many thousands have been killed
Exact numbers of the casualties for the war against IS are not available.
The Syrian Observatory for Human Rights, a UK-based monitoring group, has documented the deaths of 364,792 people, including 110,687 civilians, in Syria since the country’s civil war began in 2011.
The UN says at least 30,839 civilians have been killed in acts of terrorism, violence and armed conflict since 2014. But Iraq Body Count, an organisation run by academics and peace activists, put the civilian death toll at more than 70,000.
How IS emerged and spread
The jihadists exploited chaos and divisions within both Syria and Iraq.
IS grew out of al-Qaeda in Iraq, which was formed by Sunni Arab militants after the US-led invasion in 2003 and became a major force in the country’s insurgency.
In 2011, the group – now known as Islamic State in Iraq (ISI) – joined the rebellion against President Assad in Syria, where it found a safe haven and easy access to weapons.
At the same time, it took advantage of the withdrawal of US troops from Iraq, as well as widespread Sunni anger at the sectarian policies of the country’s Shia-led government.
In 2013, ISI began seizing control of territory in Syria and changed its name to Islamic State in Iraq and the Levant (Isis or Isil).
The following year, Isis overran large swathes of northern and western Iraq, proclaimed the creation of a “caliphate”, and became known as “Islamic State”.
A subsequent advance into areas controlled by Iraq’s Kurdish minority, and the killing or enslaving of thousands of members of the Yazidi religious group, prompted the US-led coalition to begin air strikes on IS positions in Iraq in August 2014.
Millions of refugees have fled
At least 6.6 million Syrians have been internally displaced, while another 5.6 million have fled abroad – more than 3.5 million of them have sought refuge in Turkey, and almost one million in Lebanon and almost 700,000 in Jordan.
Many Syrians have sought asylum in Europe, with Germany taking the greatest number.
In Iraq, the number of displaced people has fallen below 2 million for the first time since December 2013.
By September 2018 the International Organization for Migration estimated nearly four million people had returned home.
But the UN reports that a lack of jobs and destruction of property and limited access to services are still preventing many people from returning to their homes.
What next for IS?
One recent US report said there were still as many 14,000 IS militants in Syria and as many as 17,100 militants in Iraq, where they no longer fully control any territory.
UN experts meanwhile estimate that there are between 3,000 and 4,000 IS militants in Libya and about 4,000 in Afghanistan. The group also has a presence in South-East Asia, West Africa, Egypt’s Sinai peninsula, Yemen, Somalia and the Sahel.
In Iraq and Syria many militants have shifted tactics and returned to their insurgent roots, carrying out bombings, assassinations and kidnappings while attempting to rebuild their networks.
Individuals inspired by the group’s ideology continue to carry out attacks in Europe and elsewhere.
The strategic intelligence Soufan group carried out a study in October 2017 which estimated that about 5,600 IS fighters had returned home to 33 countries around the world.
The greatest number, about 900, had returned to Turkey. About 1,200 had returned to the European Union – including 425 to the UK, and about 300 each to Germany and France.
Hundreds of other foreign fighters are being held by the SDF in Kurdish-controlled north-eastern Syria. The US has called other countries to take back their own nationals for prosecution.