Which countries have been involved in the war and why?

A stunning breakthrough by Syrian rebels ended Bashar al-Assad’s decades-long rule, with opposition forces seizing the capital and forcing the president to flee on 8 December.

The overthrow followed a 13-year civil war, which began after Assad crushed pro-democracy protests, killing more than half a million people and displacing millions more, and embroiled international powers and their proxies.

The world is now watching how Syria’s political landscape shapes up following the overthrow of the half-century rule of the Assad family.

Among those who have a personal interest in the conflict and the future of the country are, on the one hand, Russia and Iran – who supported Assad – and, on the other, the US and Turkey, who supported to different rebel groups.

Here we explore how these countries, along with Israel, have played a role in Syria and could continue to do so.

During the Syrian civil war, Turkey has supported opposition forces, mainly the Syrian National Army (SNA), by providing weapons, military and political support.

Syria’s northern neighbor has been of primary concern using rebels to contain the Kurdish YPG militiawhich Turkey accuses of being an extension of a Kurdish rebel group banned in the country. Turkey also wants the roughly three million Syrian refugees living in its country to return home.

The YPG is the largest militia of another rebel group, the US-backed, Kurdish-led Syrian Democratic Forces (SDF) alliance.

During the war, Turkish troops and allied rebels representatives of stretches of territory of these groups along Syria’s northern border.

Turkey has also become politically involved. In 2020, Turkey and Russia negotiated a ceasefire halting a government push to retake Idlib, a rebel stronghold in the northwest.

Idlib has been administered since 2017 under the so-called government by the Islamist militant group Hayat Tahrir al-Sham (HTS), who led the rebels who eventually toppled Assad.

Many believe the offensive could not have happened without Turkey’s blessing. Turkey has denied supporting HTS.

Meanwhile, the conflict in northern Syria continues: when Assad fell, the SNA launched a separate assault on SDF-held areas.

Russia already had a decades-long relationship with the Assad government and had military bases there before the civil war.

Russian President Vladimir Putin used his country’s presence in Syria and support for Assad to challenge Western power and dominance in the region.

In 2015, Russia launched an air campaign and sent thousands of troops in support of the Assad regime.

in returnRussia received 49-year leases on an air base and a naval base, which provided crucial hubs in the eastern Mediterranean for transferring military contractors in and out of Africa.

This marked an important stage in Russia’s attempt to assert itself as a global power, having previously focused its efforts on nations formerly in the Soviet bloc.

But fighting a war in Ukraine from 2022 worried the Assad ally, contributing to the Syrian army’s rapid defeat by rebel groups in late November and early December.

Assad and his family were granted asylum in Moscow after fleeing Damascus, Russian media reported.

After Syria’s 2011 pro-democracy protests met with force, then-U.S. President Barack Obama criticized the Assad government, but only the U.S. got involved militarily to fight the Islamic State (IS).

A US-led global coalition has carried out airstrikes and deployed special forces since 2014 to help the Kurdish-led SDF rebel alliance capture territory formerly held by IS militants in the northeast.

After the fall of the Assad government, the US Govt said it was carried out dozens of airstrikes against IS camps and operatives in central Syria to ensure that IS could not take advantage of the volatile situation.

However, President-elect Donald Trump, who takes office in January, said Syria is a ‘mess’ the US should stay out. When Trump was president in 2019, he withdrew U.S. troops from Syria, a move his officials gradually reversed.

The US currently has around 900 troops in Syria.

Iran and Syria they have been allies since Iran’s Islamic revolution in 1979. Syria supported Iran during the Iran-Iraq war of the 1980s.

During the Syrian civil war, Iran is believed to have deployed hundreds of troops and spent billions of dollars to help Assad.

Thousands of Shia Muslim fighters armed, trained and financed by Iran – mostly from the Lebanon-based Hezbollah movement, but also from Iraq, Afghanistan and Yemen – have also fought alongside the Syrian army.

But, similar to Russia, Hezbollah has been weakened by the conflict with Israel in Lebanon, likely hastening the downfall of the Syrian military.

Israel shares a border with Syria. In the 1967 Six-Day War, Israel seized the Golan Heights, about 60 km (40 miles) south of Damascus, from Syria before annexing it in 1981. The annexation is not recognized by the UN and many other countries.

Israel has carried out airstrikes against Iran-linked targets in Syria during the war, although it rarely recognizes these strikes.

Since the rebels toppled Assad, Israel has carried out hundreds of attacks all over Syria. Targets include Syria’s military infrastructure, naval fleet and weapons production sites.

Israel said it is acting to prevent weapons falling “into the hands of extremists”.

Israeli forces have also done so seized the demilitarized buffer zone in the Golan Heights and might have diverted to nearby Syrian territory.

BBC Verify geolocated an image of an IDF soldier located just over half a kilometer beyond the buffer zone, inside Syria, on a hillside near the village of Kwdana.