Why is Syria at War and Who is Fighting? A Brief History of the Syrian Conflict before Trump's Military Intervention

A Syrian national flag flutters as Qasioun mountain is seen in the background from Damascus, Syria April 7, 2017. Omar Sanadiki/Reuters

Syrian President Bashar al-Assad has joined his allies, Russia and Iran, in condemning U.S. Navy airstrikes on a Syrian airbase, arguing that Washington acted on false reports and committed a deadly act of aggression.

Assad's office released a statement saying the attack had only "increased Syria's resolve to hit those terrorist agents, to continue to crush them, and to raise the pace of action to that end wherever they area," according to an online statement. The attack was ordered by President Donald Trump and came less than 72 hours after footage emerged of an alleged chemical attack on civilians. The U.S. and other Western nations have blamed the chemical attack on Assad. Trump's move marked the first intentional strike by U.S. forces on the Syrian military in the six-year conflict that has pitted various local and international forces against one another.

The conflict began in 2011 when massive protests swept through the capital and other major cities, demanding sweeping reforms to the government. A month later these demonstrations began calling for the overthrow of Assad, who responded by deploying security forces nationwide to maintain stability. Violent clashes erupted and the opposition began to organize an armed struggle against the state. This movement was supported by Western and Gulf Arab nations, who accused Assad of violently oppressing his people.

Over the course of the next year, armed rebels began taking large stretches of territory and some major urban centers such as Aleppo, Syria's commercial center. As the insurgency grew, however, so did the influence of jihadist organizations such as Al-Qaeda over the rebels' ranks. In 2013, the head of the Islamic State of Iraq, a jihadist organization formerly known as Al-Qaeda in Iraq and led by influential Sunni Muslim cleric Abu Bakr al-Baghdadi, announced he would unite his organization with Al-Qaeda's franchise in Syria, the Nusra Front, which had become one of the most powerful groups fighting to overthrow Assad. Nusra's head, Abu Mohammad al-Julani, refused this merger, but Baghdadi's group stormed Syria anyway, branding itself as the Islamic State of Iraq and Syria (ISIS) or the Islamic State of Iraq and the Levant (ISIL).

ISIS' entrance signaled a new phase in the conflict. Jihadist influence became rampant among the armed opposition and the Pentagon began to reevaluate its support of rebel groups, some of which had become absorbed into the ranks of Al-Qaeda and ISIS, bringing U.S. training and weapons with them. Former President Barack Obama shifted the focus of U.S. policy from removing Assad to battling the spread of ISIS, which had taken over a large portion of the country. In 2014, the U.S. began conducting airstrikes on ISIS in Syria.

The following year, Russia entered the conflict. Syria's relationship with Russia dated back to the 1970s and Moscow had politically supported Assad throughout the war. Russia's intervention came at the direct request of Assad, as his military and its allies struggled to cope with waves of jihadist militants. Russia's intervention marked a turning point for the Syrian army, which began to reverse years of territorial losses and retook major strategic cities such as Homs and Aleppo from ISIS and other opposition groups.

Obama criticized Russian President Vladimir Putin for his backing of Assad, whom he accused of committing war crimes. Russia has, in turn, charged the U.S. with supporting terrorism by undermining the Syrian army's mission and backing rebel groups. The international powers have mostly avoided one another, however, and focused on battling ISIS and other jihadists. The U.S. began to scale back its support of rebels as radical Islamist influence grew and shifted its support to the Syrian Democratic Forces (SDF), a Kurd-dominated coalition of Arabs and ethnic minorities in Syria.

The SDF began clashing with not only ISIS, but also rebels, who received newfound support from another international actor, Turkey. Ankara has considered the SDF a terrorist organization for its links to militant Kurdish nationalist groups in Turkey and has criticized both the U.S. and Russia for supporting it. As President Donald Trump took office earlier this year, Russia and the U.S.' mission in Syria appeared to more or less align. U.S. and Russian forces both deployed in the SDF-controlled town of Manbij to prevent a Turkish-sponsored rebel advance; as recently as last week, Secretary of State Rex Tillerson and U.S. ambassador to the U.N. Nikki Haley said the U.S. would officially abandon its Obama-era stance on mandating Assad's removal for peace talks.

Trump's views changed, he said, after the alleged chemical attack on rebel-held Idlib. Trump had both accused Obama of not taking action after a similar incident in 2013 and had also warned the former leader not to intervene in Syria at various times, leaving observers unclear as to how the relatively new president would react. While the White House has suggested that Friday's strikes were merely a warning to Assad and his allies not to pursue chemical weapons attacks and would not signal a larger change in U.S. policy, the move has been received by Syria, Russia and Iran as a new act of aggression in a war that has killed hundreds of thousands of people and displaced millions more across the globe.