Despite the collapse of Islamic State last year and a widespread international perception that Syria's President Bashar al-Assad is winning the war, there have been major new escalations around the country.
Seven years in, Syria's conflict has killed hundreds of thousands, driven millions from their homes, disturbed the regional balance of power and dragged in foreign nations whose rivalry has upset existing alliances.
It is that international element that has helped transform the war from a straight fight between Assad and rebel forces trying to overthrow the president into a mess of overlapping conflicts.
In the process, Syria has become a battleground for geopolitical rivalries, pitching the United States against Russia and Iran against Israel while inflaming the rift between Sunni and Shi'ite Muslims in the Middle East.
What do the different sides want?
ASSAD's goal is clear: the complete recapture of all parts of Syria and the restoration of his government's rule.
His strongest ally RUSSIA turned the war in his favour by sending its air force to help him in 2015. But it may be readier than Assad to agree concessions with his adversaries. It has brought Iran and Turkey into talks to stabilise the crisis by agreeing "de-escalation zones" meant to stop the fighting.
Assad's other main backer is IRAN along with allied militias such as HEZBOLLAH from Lebanon. Tehran says it is fighting anti-Shi'ite Sunni militancy. But Iran's critics say it wants to cement regional power with a "land bridge" extending from Iran through Iraq and Syria to Lebanon.
The most fearsome Sunni militant group is ISLAMIC STATE. Its self-declared caliphate is now in tatters. But it still holds pockets of desert and will take advantage of any new conflict to undermine stability and retake ground.
Syria's REBEL GROUPS all want to oust Assad but they are divided internally over whether they want a state based on Islam or Syrian nationalism, and sometimes fight each other. They want to keep the uprising alive, maintain foreign support and defend their remaining territory.
TURKEY was one of the biggest rebel supporters. Its main focus now, however, is driving the Kurdish YPG away from its border as it sees the militia as an extension of the PKK, a group that has waged a three-decade insurgency against Ankara.
KURDISH FORCES sandwiched between Turkey and Syria's army want to cement their autonomy in the north, where they have set up ruling councils and held elections. They want to stop Turkey or Assad attacking their territory.
The UNITED STATES helped anti-Assad rebels earlier in the war but became more focused on fighting Islamic State. It backs the SDF (Syrian Democratic Forces) alliance, whose strongest element is the Kurdish YPG. However, Washington wants to smooth the outrage this has caused its NATO ally Turkey.
Washington also wants to contain Iran as it sees the country's growing influence across the region as threat to its closest Middle East allies Israel and Saudi Arabia.
ISRAEL wants to stop any expansion of power for its mortal foes Iran and Hezbollah and keep them far from its borders.
How competing agendas have split Syria
Assad and his allies want to hasten the end of the rebels by pushing them from EASTERN GHOUTA, and are using the siege and bombardment tactics that helped them crush opposition in Aleppo, Homs and other former insurgent strongholds.
Many rebels have been pushed into northwestern IDLIB province and neighbouring areas, their biggest remaining stronghold. Turkey has sent some troops to Idlib to monitor a de-escalation zone there after talks with Russia and Iran. But a recent advance by Assad and his allies took ground in Idlib.
Turkey and allied rebels launched an assault last month against the Kurdish YPG in AFRIN, a region that is separated from a much bigger area controlled by the Kurds further east. While the United States backed the YPG in its fight against Islamic State, it has not supported it against Turkey in Afrin, calling only for Turkish restraint.
Russia had stationed troops in Afrin to help stop any Turkish assault but it also wants Ankara's cooperation in its wider peacemaking efforts inSyria and pulled them out. The Kurds then turned to Assad for help despite their rivalry. Assad has not sent his army there, but did dispatch allied militias linked to Iran to help the Kurds against Turkey.
Turkey may turn next to attack the YPG near MANBIJ, 100 km (60 miles) to the east of Afrin. It is the only Kurdish-led area west of the Euphrates other than Afrin. But unlike Afrin, there are U.S. forces in Manbij who have fired on Turkish-backed rebels and say they will defend themselves and their SDF allies.
The United States is also present in oil-rich EASTERN SYRIA, where the SDF and a rival campaign by Assad and his allies have each taken swathes of ground from Islamic State. Despite the YPG's request for Assad's help in Afrin, there is no sign of agreement between them in the east, where U.S. jets backing Kurdish-led forces have struck Assad's allies.
Potentially the most explosive area of conflict in Syria is the SOUTHWEST, where rebels still hold a swathe of territory near the Israeli-occupied Golan Heights. The United States, Russia and Jordan, whose border is nearby, agreed a de-escalation zone there last year.
But Assad and allied militia with ties to Iran and Hezbollah waged a weeks-long ground campaign there last year and remain stationed in the area. This is anathema to Israel, which sees the militias as Iranian pawns.
Israel shot down an Iranian drone this month and responded with air raids in which one of its jets was downed. It showed the risk of fighting inSyria leading to a wider confrontation between Israel and Iran that could also expand to Hezbollah in Lebanon.
Any war between Israel and Iran and its allies would also risk dragging in the United States.
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