Foreign fighters in the Syrian civil war had come to Syria and joined all four sides in the war. In addition to Sunni foreign fighters arriving to defend the Islamic State of Iraq and the Levant or join the Syrian rebels, Shia fighters from several countries have joined pro-government militias in Syria (assisted by private military contractors), and leftists have become foreign fighters in the Syrian Democratic Forces.Cerwyn Moore & Paul Tumelty (2008) "Foreign Fighters and the Case of Chechnya: A Critical Assessment", Studies in Conflict & Terrorism, 31:5, 412–433.
Estimates of the total number of foreign Sunnis who have fought for the Syrian rebels over the course of the conflict range from 5,000 to over 10,000, while foreign Shia fighters numbered around 10,000 or less in 2013 rising to between 15,000 and 25,000 in 2017. While more than 30,000 foreign fighters heeded the call to come to the Islamic State of Iraq and the Levant, not all of these were deployed in Syria, as the Islamic State also held a large part of Iraq for some years.
Support for rebels and the Islamic State
Sunni Jihadists Throughout 2014, with the rise of the Islamic State, the Al-Nusra Front, and other groups, their numbers drastically increased and they partnered with and absorbed Syrian rebel groups, both jihadist and non-jihadist. By 2015, foreign jihadists outnumbered Syrian jihadists and other rebels in casualty rolls (16,212 anti-government foreign jihadists were killed in 2015 compared to 7,798 Syrian anti-government rebels killed that same year), a trend that carried over into 2016 (13,297 foreign jihadists and 8,170 Syrian rebels), and 2017 (7,494 foreign jihadists and 6,452 Syrian rebels). However, although the numbers of casualties remained high in this phase, arrivals slowed: according to the United States military, foreign fighters coming to Syria and Iraq in 2013-2015 averaged 2,000 fighters per month, but by 2016, this figure had dropped to less than 500 fighters per month and decreasing.Stewart, Phil. U.S. military softens claims on drop in Islamic State's foreign fighters. Reuters. April 28, 2016. Quote: "U.S. Army Colonel Steve Warren, a Baghdad-based spokesman for the coalition, told Reuters that the official estimate is higher than the one Gersten offered, although he did not provide a precise figure. "We believe the foreign fighter flow was 2,000 at one point and is now down to a quarter or less of that," Warren said." By 2018, the proportion of foreign fighters had seriously decreased (following heavy losses in the bloody battles of 2015-2017 and an increase in interventions by foreign military forces), and Syrian rebels were once again the majority of anti-government casualties (2,746 foreign jihadists killed compared to 5,852 Syrian rebels).2018 under different titles...the death of about 23,000 persons, the displacement of hundreds of thousands others, shifts in the influence of the conflicting powers, and regional and international agreements of de-escalation and withdrawal.
Most of the foreign fighters in Syria are drawn to the jihadist ideology, although experts note that religion is not the only motivation: From ignorant novices who view the trips as a rite of passage, die-hard militants looking for combat and martyrdom, and individuals who go for humanitarian reasons but get drawn into conflict, individuals become foreign fighters for a range of reasons: boredom; intergenerational tensions; the search for greater meaning in life; perceived adventure; attempts to impress the local community or the opposite sex; a desire for increased credibility; to belong or gain peer acceptance; disillusionment with their own home country; revenge; or misguided conflict experience expectations.
Foreign fighters are drawn both to Daesh and other Islamist fighting groups, such as al-Nusra Front, Liwa al-Muhajireen wal-Ansar (which includes Chechen fighters), and (prior to 2013) Ahrar al-Sham. Jaysh al-Islam rebel leader Zahran Alloush called for foreign fighters to come to Syria, although experts report that the group does not include foreign fighters. "Somewhat distinct from other rebel organizations in Syria, Alloush's Army of Islam is purely Syrian in composition. There are no foreign fighters in its ranks, no veterans of mujahidin campaigns in Iraq or Afghanistan." On 31 May 2013, Yusuf al-Qaradawi called for a jihad against the Syrian government.
According to the Syrian Observatory for Human Rights, at least 65,726 anti-government foreign fighters (almost entirely jihadists) were killed in Syria up to May 2020, constituting nearly half of the 138,202 anti-government fighters killed by that point.Fourteen years of championing human rights in Syria Syrian Observatory for Human Rights
After the overthrow of the Assad government, many of the foreign fighters that fought for the opposition were integrated into the ranks of the recently established 84th Division, as a part of the newly reformed Syrian Army.
Leftists Although they are less numerous than those joining the Syrian Democratic Forces, there have also been leftist foreign fighters joining the Syrian rebels. The most prominent group is the Trotskyist Leon Sedov Brigade, founded by Argentine leftists who had previously fought with the Free Libyan Army, which was involved in the Battle of Aleppo.
Support for Syrian government
Shia jihadists Thousands of Shia jihadist militants have travelled to Syria from Iraq, Lebanon, Iran, Pakistan, Afghanistan, and Bahrain, fighting under various Iranian-backed militant groups like Liwa Fatemiyoun, Liwa Zainebiyoun, Hezbollah, etc. These groups fight in support of the Assad government, which is dominated by minority Alawites.
Far-right militants Several far right extremist groups in the Balkans, such as Black Lily, Golden Dawn, are supportive of the Assad government in Syria. Serbian nationalist militants have travelled to Syria and joined pro-Assad militias. Black Lily stated in 2013 that many of its members were fighting alongside the Syrian Arab Army. Neo-nazi groups like Golden Dawn and Black Lily have also perpetrated several violent attacks against Syrian refugees in Greece.
Mercenaries and private contractors There are several private military companies operating in Syria, such as the Wagner Group and the Slavonic Corps.
Support for DAANES
Hundreds of leftists have become foreign fighters in the Syrian Democratic Forces, with most joining the International Freedom Battalion of the People's Protection Units (YPG), out of a mixture of opposition to the Islamic State and willingness to defend the Autonomous Administration of North and East Syria (AANES).
Passage Most fighters in the various non-regime factions travel to Turkey first before crossing the border, with somewhat lesser contingents coming from Lebanon and even fewer from Jordan and Iraq; some use forged passports to avoid the attention of the authorities. The Islamist government of Turkey, which is occupying part of northern Syria and has been accused of collaboration with ISIL, has been repeatedly criticised for facilitating the transit of jihadists. In 2013, around 30,000 militants entered Syria via Turkey.
Fighters arriving in Syria to support the government enter at the government-controlled crossings on the Lebanese, Jordanian, and (after the Syrian Desert campaign) Iraqi borders, or take a flight to any of the international airports (only government-controlled airports have been authorised for international flights by the International Civil Aviation Organization).
SDF foreign fighters usually cross into the AANES from Iraqi Kurdistan, over the relatively porous Iraq-Syria border.
Casualties According to the Syrian Observatory for Human Rights, at least 65,726 anti-government foreign fighters (almost entirely jihadists) were killed in Syria up to May 2020, constituting nearly half of the 138,202 anti-government fighters killed by that point. Additionally, 10,045 foreign fighters on the side of the Syrian government were killed by then (1,700 Lebanese Hezbollah and 8,345 others, including 2,000+ militiamen of Liwa Fatemiyoun and 264 Russian soldiers and mercenaries), about 7% of the total casualties for the government side.Fourteen years of championing human rights in Syria The Syrian Observatory for Human Rights 76 foreigners have died fighting for the Syrian Democratic Forces, less than 1% of the total SDF dead (although many Kurds from non-Syrian parts of Kurdistan have also died, they aren't counted as foreigners by the SDF).
Reactions International organisations United Nations In November 2014, the United Nations Security Council adopted Resolution 2178, which enjoined member states to actively suppress Sunni jihadist movements and prevent the travel of their recruits.
Governments Governments have adopted a wide range of policies and measures concerning their citizens who go to fight in Syria. These differ from country to country, with some focusing on prevention, some on prosecution, some on rehabilitation and reintegration, some on deprivation of citizenship, and some tailoring their approach depending on which side their citizens fought. With a focus on more preventative measures, countries have developed programs that focus on inter-cultural and inter-religious dialogue, as well the use of counter-narratives.
Syrian government On 3 July 2013, it was reported that Syrian aircraft had dropped leaflets over areas in Idlib province calling on both rebels to turn themselves over to the authorities and for foreign fighters to return to their countries. Later that month, the Syrian government passed a law that would punish anyone entering the country illegally with jail time and a fine of LS 5,000,000–10,000,000.
Turkey
Turkish involvement in the Syrian civil war is considerable, especially since 2016, when it began the Turkish occupation of northern Syria. Most of the foreign jihadists who travel to Syria enter through Turkey. Turkey was said to be concerned about the presence of radical jihadists on their border with Syria. In a 2015 nationwide poll in Turkey, 3.2 per cent of respondents said they knew someone who had joined the Islamic State. The Turkish state has been repeatedly accused of collaboration with ISIL. Of the thousands of Turks who fought for the Islamic State and then returned to Turkey, only a few have been convicted.
Many Kurdish citizens of Turkey have joined the People's Protection Units (YPG), and Turkish communists make up the majority of the International Freedom Battalion.
In 2013, Turkish President Abdullah Gul said Syria risked becoming "Afghanistan on the shores of the Mediterranean" and that Turkey could become a Mediterranean Pakistan.
Saudi Arabia
Saudi Arabian involvement in the Syrian Civil War dates from the early days of the war, and by 2013 it was the main financier and supplier of Sunni Islamist factions. Thousands of Saudis travelled to Syria to fight, almost all for the Sunni rebels.
Grand Mufti of Saudi Arabia Abdul-Aziz ibn Abdullah Al ash-Sheikh called for Syrians to be "enable[d]" to protect themselves. He also said of fighters going to the country that "this is all wrong, it's not obligatory. I do not advise one to go there ... you will be a burden to them, what they want from you is your prayer. These are feuding factions and one should not go there. I do not advise one to go there. ... Going to a land that you do not know and without experience, you will be a burden to them, what they want from you is your prayer. Muslims should be fearful of God and not deceive young Muslims and exploit their weakness and lack of insight and push them to an abyss. I advise them to advise as they would advise their sons." This was interpreted as an expression of government fear of its citizens returning home and using the skills they learnt against the Saudi state.
Egypt