Despite the collapse of Islamic State last year and a widespread international perception that Syria's President Bashar 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 Shiite Muslims in the Middle East.
But what is it exactly that the different parties involved in the Syrian quagmire 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, has turned the war around in his favor by sending its air force to help him in 2015. But it may be readier than Assad to agree to concessions with his adversaries. Russia has brought Iran and Turkey into talks to stabilize the crisis by agreeing "de-escalation zones" meant to stop the fighting.
Assad's other main backer is Iran, along with allied militias and regional proxy, the Lebanon-based Hezbollah. Tehran says it is fighting anti-Shiite 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, which straddled parts of Iraq and Syria, is now in tatters, but it still holds pockets of desert land and will take advantage of any new conflict to undermine stability and retake ground.
Syria's rebel groups all want to unseat 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, once the rebels' biggest supporter, is now focused on 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 has helped anti-Assad rebels earlier in the war but became more focused on fighting Islamic State. It backs the 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 a threat to its closest Middle East allies Israel and Saudi Arabia.
Israel, for its part, wants to stop any expansion of power for its mortal foes Iran and Hezbollah and keep them far from its borders.
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 neighboring 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 U.S. 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 in Syria 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, some 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 U.S. 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 its southwest, where rebels still hold a swathe of territory near the the Golan Heights border with Israel. The U.S., Russia and Jordan, whose border is nearby, agreed to form 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 that breached Israeli airspace earlier this month, and responded with air raids to the incursion in which one of its jets was downed. It showed the risk of fighting in Syria 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.
