The War in Iraq (2013–2017) was an armed conflict between Iraq and its allies and the Islamic State. Following December 2013, the insurgency escalated into a full-scale war following clashes in parts of western Iraq, which culminated in the Islamic State offensive into Iraq in June 2014, leading to the capture of the cities of Mosul, Tikrit and other cities in western and northern Iraq by the Islamic State. Between 4–9 June 2014, the city of Mosul was attacked and later fell; following this, Prime Minister Nouri al-Maliki called for a national state of emergency on 10 June. However, despite the security crisis, Iraq's parliament did not allow Maliki to declare a state of emergency; many legislators boycotted the session because they opposed expanding the prime minister's powers. Ali Ghaidan, a former military commander in Mosul, accused al-Maliki of being the one who issued the order to withdraw from the city of Mosul. At its height, ISIL held 56,000 square kilometers of Iraqi territory, containing 4.5 million citizens.
The war resulted in the forced resignation of al-Maliki in 2014, as well as an airstrike campaign by the United States and a dozen other countries in support of the Iraqi military, participation of American and Canadian troops (predominantly special forces) in ground combat operations, a $3.5 billion U.S.-led program to rearm the Iraqi security forces, a U.S.-led training program that provided training to nearly 200,000 Iraqi soldiers and police, the participation of the military of Iran, including troops as well as armored and air elements, and military and logistical aid provided to Iraq by Russia. On 9 December 2017, Prime Minister Haider al-Abadi announced victory over the Islamic State. The Islamic State switched to guerrilla "hit and run" tactics in an effort to undermine the Iraqi government's effort to eradicate it. This conflict is interpreted by some in Iraq as a spillover of the Syrian civil war. Other Iraqis and observers see it mainly as a culmination of long-running local sectarianism, exacerbated by the 2003–2011 Iraq War, the subsequent increase in anti-Sunni sectarianism under Prime Minister al-Maliki, and the ensuing bloody crack-down on the 2012–2013 Iraqi protests.
The Iraqi Armed Forces, Kurdish Peshmerga, Sunni insurgent and tribal groups and various Turkmen Muslim, Assyrian Christian, Yezidi, Shabaki, and Armenian Christian forces faced the Islamic State of Iraq and the Levant. Although some 35,000 Kurdish Peshmerga were incorporated into the Iraqi Armed Forces, most Peshmerga forces operated under the command of the President of Kurdistan Region in the federal Kurdistan Region of Iraq. Assyrian forces included: Nineveh Plain Protection Units, Nineveh Plain Forces, Babylon Brigades, Kataib Rouh Allah Issa Ibn Miriam, Qaraqosh Protection Committee and Dwekh Nawsha.
In the course of their Anbar campaign, ISIL militants and their Baathist allies seized at least 70% of Al Anbar Governorate by June 2014, including the cities of Fallujah, Al Qaim, and half of the provincial capital of Ramadi. ISIL forces also infiltrated Abu Ghraib in Baghdad Governorate.
In early June 2014, following further large-scale offensives in Iraq, ISIL and their allies seized control of Mosul, the second most populous city in Iraq, the nearby town of Tal Afar and most of the surrounding Nineveh Governorate. ISIL also captured parts of Kirkuk and Diyala Governorates and Tikrit, the administrative center of the Salahuddin Governorate, with the ultimate goal of capturing Baghdad, the Iraqi capital. ISIL was believed to have only 2,000–3,000 fighters up until the Mosul campaign, but during that campaign, it became evident that this number was a gross underestimate. There were also reports that the number of Sunni groups in Iraq that were opposed to the predominantly Shia government had joined ISIL, thus bolstering the group numbers. However, the Kurds—who are mostly Sunnis—in the northeast of Iraq, were unwilling to be drawn into the conflict, and there were clashes in the area between ISIL and the Kurdish Peshmerga.
On 12 June 2014 ISIL killed 1,700 unarmed Iraqi Air Force cadets who were caught trying to flee to safety and released many images of mass executions via its Twitter feed and various websites.
In late June, ISIL militants captured two key crossings in Anbar, a day after seizing the border crossing at Al-Qaim. According to analysts, capturing these crossings could aid ISIL in transporting weapons and equipment to different battlefields. Two days later, the Syrian Air Force bombed ISIL positions in Iraq near the Al-Qaim border post. Iraqi Prime Minister Nouri al-Maliki stated: "There was no coordination involved, but we welcome this action. We welcome any Syrian strike against Isis because this group targets both Iraq and Syria."
At this point, The Jerusalem Post reported that the Obama administration had requested US$500 million from the U.S. Congress to use in the training and arming of "moderate" Syrian rebels fighting against the Syrian government, in order to counter the growing threat posed by ISIL in Syria and Iraq.
On 29 June, ISIL announced the establishment of a new caliphate. Abu Bakr al-Baghdadi was appointed its caliph, and group formally changed its name to the Islamic State. Four days later, Abu Bakr al-Baghdadi, the self-proclaimed caliph of the new Islamic State, said that Muslims should unite to capture Rome in order to "own the world." He called on Muslims all over the world to unite behind him as their leader.
On 24 July, ISIL blew up the Mosque and tomb of the Prophet Yunus (Jonah) in Mosul, with no reported casualties. Residents in the area said that ISIL had erased a piece of Iraqi heritage. Jonah's tomb was an important holy site in the Jewish heritage as well. A few days later, ISIL also blew up the Nabi Shiyt (Prophet Seth) shrine in Mosul. Sami al-Massoudi, deputy head of the Shia endowment agency which oversees holy sites, confirmed the destruction and added that ISIL had taken artifacts from the shrine to an unknown location.
In an August offensive, ISIL captured Sinjar after it was abandoned by the Peshmerga, and a number of other towns in the north of the country. Almost 200,000 civilians, mostly Yazidis, managed to flee from the fighting in Sinjar city, about 50,000 of them fled into the Sinjar Mountains, where they were trapped without food, water or medical care, facing starvation and dehydration. They had been threatened with death if they refused conversion to Islam. A UN representative said that "a humanitarian tragedy is unfolding in Sinjar." In addition, during this latest offensive, the Islamic State advanced to within 30 km of the Iraqi Kurdish capital of Erbil in northern Iraq.
Prompted by the siege and killings of the Yazidis, on 7 August, President Obama authorized targeted airstrikes in Iraq against ISIL, along with airdrops of aid. The UK offered the U.S. assistance with surveillance and refueling, and planned humanitarian airdrops to Iraqi refugees. The U.S. asserted that the systematic destruction of the Yazidi people by the Islamic State was genocide. The Arab League also accused the Islamic State of committing crimes against humanity.
On 13 August, U.S. airstrikes and Kurdish ground forces broke the ISIL siege of Mount Sinjar. Also, five days later, Iraqi Special Operations Forces with Kurdish Peshmerga and U.S. air support, overran ISIL militants and reclaimed the Mosul Dam.
On 31 August, the United States, France, United Kingdom and Australia began humanitarian aid drops of food, water and medical supplies to help prevent a potential massacre against the Shia Turkmen minority in Amirli. The U.S. also carried out air strikes on ISIL positions around and near Amirli. Iraqi officials stated that they had reached Amirli and broken the siege and that the military was fighting to clear the areas around the town. This is known to be the first major turning point against ISIL in Iraq.
In September, the United States sent an additional 250 troops to protect American personnel, while the first engagement of the British military against ISIL targets took place when a British Panavia Tornado jet dropped a Paveway IV bomb on "a heavy weapon position" operated by ISIL in northwest Iraq at the end of the month. In addition, Australia offered 200 special forces to the Kurds and 600 Australian troops landed in the UAE. The following month, Australia authorized its special forces troops to go to Iraq as part of the anti-ISIL coalition that day, as well as authorizing airstrikes.