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Hay’at Tahrir al Sham (formerly known as Jabhat al-Nusra and JabhatFateh al-Sham)
The group that became Jabhat al-Nusra was created on the orders of Abu Bakr al-Baghdadi in 2011 as an al-Qaeda's branch in Syria. However, after al-Baghdadi's organization (then known as al-Qaeda in Iraq (AQI)) falsely declared that Jabhat al-Nusra had merged into AQI relations between the two organizations soured. Since that point, the two have become openly hostile to each other. The group rebranded itself as Jabhat Fateh al-Sham in the summer of 2016 (and claimed to sever its ties with al-Qaeda), but as al-Qaeda fighters still fight along side them, most observers still consider them tied to al-Qaeda.
This group engages in terrorist attacks (including suicide bombings), kidnapping, and hostage-taking.
The US State Department considers the group a terrorist organization.
They have fought against the Syrian government, the Free Syrian Army, ISIS, and a variety of other groups in the conflict.
In January 2017, Jabhat Fateh al-Sham merged with four other Jihadist groups into an organization known as Hay’at Tahrir al Sham, led by Abu Jabir (the former leader of Ahrar al-Sham).
According to the Brookings Institute (July 2016), the group has 7,000 fighters.
Resources on on Hay’at Tahrir al Sham (formerly known as Jabhat al-Nusra and Jabhat Fateh al-Sham)
Ahrar al-Sham was formed in late 2011 by former Syrian prisoners who the al-Assad government released. They have been hostile to the al-Assad regime for most of the period since, but they have, at times, signed ceasefires with the Syrian government.
The group is a Salafist, Islamist organization which wants to create a Sunni Islamic state in Syria.
The group has consistently worked to unify the disparate Syrian Islamist groups and are one of the co-founders of Jaysh al-Fateh (a prominent Syrian Islamist coalition).
Turkey, Qatar, and Saudi Arabia provide support to Ahrar al-Sham.
Ahrar al-Sham initially worked with ISIS, but has fought them since 2014 when relations broke down between the groups and ISIS killed most of Ahrar al-Sham's leadership.
Russian, Lebanon, Egypt, Iran, Syria, and the UAE consider Ahrar al-Sham a terrorist organization.
Jaysh al-Islam has put forwad contradictory public statements regarding their ultimate goals.
They have claimed to desire an Islamic state under Shari'a law, but on other occasions claimed to desire a non-sectarian, technocratic state (The Daily Beast, Dec. 2015).
Their former leader, Zahran Alloush, had also called for the cleansing of Shiites and Alawites from Damascus (cited in Syria Comment, Dec. 2013).
Russian, Lebanon, Egypt, and Syria consider Jaysh al-Islam a terrorist organization.
The Institute for the Study of War (Mar. 2016) claimed they were "second largest Salafi Jihadist opposition faction in Syria" with between 17,000 and 30,000 fighters.
Bloomberg (Sept. 2016) estimated that they had between 12,000 and 20,000 fighters.