War against the Islamic State

Many states began to intervene against the Islamic State, in both the Syrian civil war and the War in Iraq (2013–2017), in response to its rapid territorial gains from its 2014 Northern Iraq offensives, universally condemned executions, human rights abuses and the fear of further spillovers of the Syrian civil war. In later years, there were also minor interventions by some states against IS-affiliated groups in Nigeria and Libya. All these efforts significantly degraded the Islamic State's capabilities by around 2019–2020. While moderate fighting continues in Syria, as of 2025, IS has been contained to a small area and force capability.

In mid-June 2014, Iran, according to American and British information, started flying drones over Iraq, and, according to Reuters, Iranian soldiers were in Iraq fighting IS. Simultaneously, the United States ordered a small number of troops to Iraq and started flying crewed aircraft over Iraq. In July 2014, according to the International Institute for Strategic Studies, Iran sent Sukhoi Su-25 aircraft to Iraq, and Hezbollah purportedly sent trainers and advisers to Iraq in order to help Shia militias to monitor IS's movements. In August 2014, the US and Iran separately began a campaign of airstrikes on IS targets in Iraq. Since then, fourteen countries in a US-led coalition have also executed airstrikes on IS in Iraq and in Syria. Starting from September 2014, United States began closely co-operating with Saudi Arabia and Jordan to wage a co-ordinated aerial bombing campaign against IS targets across Iraq and Syria.

In September 2015, Russian forces launched their military intervention in Syria to support that country's ally Bashar al-Assad in the fight against the Islamic State. Although Moscow officially portrayed its intervention as an anti-IS campaign and publicly declared support for the "patriotic Syrian opposition", the vast majority of its bombings were focused on destroying bases of the Syrian opposition militias of the Free Syrian Army (FSA) and Southern Front. On the other hand, United States and its Western allies have been opposed to the former Ba'athist regime for its purported state-sponsorship of terrorism, violent repression of Syrian revolution and extensive use of chemical weapons. The US-led coalition trained, equipped and supported secular Free Syrian and Kurdish militias opposed to the Assad government during its anti-IS campaign. In the months following the beginning of both air campaigns, IS began to lose ground in both Iraq and Syria. Civilian deaths from airstrikes began to mount in 2015 and 2016. In mid-2016, the US and Russia planned to begin coordinating their airstrikes; however, this coordination did not materialize.

As of December 2017, IS was estimated to control no territory in Iraq, and 5% of Syrian territory, after prolonged actions. On 9 December 2017, Iraq declared victory in the fight against ISIL and stated that the War in Iraq was over. On 23 March 2019, IS was defeated territorially in Syria after losing the Battle of Baghuz Fawqani, after which the group was forced into an insurgency. IS's leader, Abu Bakr al-Baghdadi, died during a US special operations raid in northern Syria in October 2019 and was succeeded by Abu Ibrahim al-Hashimi al-Qurashi. The United Nations estimated in August 2020 that over 10,000 IS fighters remained in Syria and Iraq, mainly as sleeper cells.