In September 2015, Russia intervened militarily in the conflict on behalf of the Assad regime. The attacks carried out from planes and ships were not primarily directed – as initially announced – against IS, but also against other groups in opposition to Assad. The Kurdish YPG formed the Syrian Democratic Forces (SDF) Alliance in October 2015 with mainly Christian-Arab militias. After the Paris terrorist attacks on November 13, 2015, France intensified its air strikes on IS positions, which it began in September 2015. In December 2015, the UK expanded its military operation against ISIS in Iraq to include air strikes in Syria.
In addition, international efforts to find a political solution to the conflict were intensified at four meetings of the Syria support group in October / November 2015 in Vienna, in December 2015 in New York and in February 2016 in Munich. The five UN veto powers, Germany, Iran, Saudi Arabia, Turkey and other states agreed in Vienna, among others. on the preservation of the state of Syria, negotiations between the regime and selected rebel groups and a ceasefire. At a conference in Riyadh in December 2015, the opposition agreed on an action plan to create a pluralistic, democratic state based on the rule of law. In addition to the “National Coalition” and the Free Syrian Army, Islamists such as Jaish al-Islam and Ahrar al-Sham also played at the meeting. The Kurdish opposition, the al-Nusra Front (after the separation from al-Qaeda from July 2016 Jabhat Fatah al-Sham) and the IS remained excluded. A high negotiating council was constituted as the representative body of the. On December 18, 2015, the UN Security Council unanimously passed resolution 2254, which supported the Vienna resolutions. The January 2016 in GenevaTalks on a peace settlement that had begun (Geneva III) were suspended on 3.2.2016 after protests by the High Negotiating Council against Russian air strikes in northern Syria. In February / March 2017, new talks took place in Geneva (Geneva IV, V) under the auspices of the UN. They did not make any substantial progress either.
Turkey began shooting at Kurdish positions in Syria on February 13, 2016. Finally, on February 22, 2016, the USA and Russia agreed to cease all hostilities as of February 27, 2016. The al-Nusra Front and IS were excluded from the agreement. The Syrian government approved the ceasefire on February 23, 2016. In March 2016, government troops succeeded in retaking Palmyra, which, however, fell back into the hands of IS from October 2016 to March. In October 2017, however, after months of fighting, IS was driven out of its “capital”, Raqqa. The fighting between the anti-IS alliance, SDF and Syrian government troops against the last IS bases in the southeast on the border with Iraq dragged on until March 2019.
With the support of the Russian Air Force and Shiite militias, the Syrian government troops were able to make military progress in the battle for Aleppo in July / August 2016 and largely enclose the eastern districts held by the rebels. The battle for Aleppo led to a humanitarian catastrophe that left thousands of victims. On December 23, 2016, the government regained full control of the city. Tens of thousands of civilians and rebels had been evacuated from East Aleppo in the previous days. Government forces regained full control of Homs in May 2017.
In order to prevent the expansion of the Kurdish sphere of influence and to fight the IS, Turkey intervened since August 2016 with the “Euphrates Shield” ground offensive in northern Syria. On December 20, 2016, Turkey, Russia and Iran held a meeting of their foreign and defense ministers in Moscow and offered themselves as guarantor powers for a peace solution in Syria. With the so-called Astana Process, a new diplomatic format was established from September 2017 as a supplement to or in competition with the Geneva negotiations. An approach to a satisfactory conflict resolution was not achieved in either negotiation format. However, on October 31. In 2019, a committee made up of representatives of the Assad regime, the opposition and civil society convened for the first time in Geneva to work out a new constitution for Syria.
On the sidelines of the G20 summit in Hamburg, the USA and Russia agreed a ceasefire for the southwestern parts of Syria, which came into force on July 9, 2017. In June 2018, however, the Syrian army captured much of Dara province. In May 2017, Russia, Turkey and Iran had already decided to set up so-called de-escalation zones in Astana, in which the violence should be ended through agreements. In fact, they were only a preliminary stage to the military conquest by the Assad regime and its allies.
In January 2018, Turkey began an offensive against the Kurdish YPG-controlled Afrin region with “Operation Olive Branch” in association with parts of the Free Syrian Army (FSA), which led to tensions with NATO partner USA. With the support of their allies, Syrian government troops launched an attack on the rebel stronghold of East Ghouta near Damascus in February 2018. After a suspected use of poison gas on April 7, 2018 in Duma near Damascus, the USA, France and Great Britain attacked targets in Syria with rockets on April 14, 2018. There had been multiple operations with chemical weapons since 2017, the heaviest on April 4, 2017 with at least 83 deaths in Khan Sheikhoun (Idlib province), according to the UN’s armed forces of the Assad regime.