Rebel forces have launched their biggest offensive against the Syrian government in years.
In just over a week, they established control over the second largest city in the country, Aleppo, the city of Hama, a they started to enter and to the third largest city, Homs.
In southern Syria near the Jordanian border, local rebels have reportedly captured much of Deraa, the birthplace of the 2011 uprising against President Bashar al-Assad.
The surprise offensive to the north was met with very little resistance by the Syrian army, which withdrew its forces from Aleppo, as well as from Hama and other areas.
The attack was led by the Islamist militant group Hayat Tahrir al-Sham (HTS), which has a long and involved history in the Syrian conflict.
The United Nations, the USA, Turkey and other countries have declared HTS a terrorist organization.
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HTS was founded under another name, Jabhat al Nusra, in 2011 as a direct branch of Al Qaeda.
The leader of the self-proclaimed Islamic State (IS) Abu Bakr al-Baghdadi participated in its founding.
It was considered one of the most effective and deadly groups fighting against President Assad.
But HTS's main driving force seemed to be its jihadist ideology rather than revolutionary fervor, which at the time was at odds with the main rebel coalition under the slogan Free Syria.
And in 2016, the group's leader, Abu Muhammad al-Jawlani, publicly distanced himself from Al-Qaeda, disbanded Jabhat al-Nusra and founded a new organization, which took the name Hayat Tahrir al-Sham when it merged with several other similar groups a year later.
For some time now, HTS has held its main stronghold in the northwestern province of Idlib, where it is de facto local administration, although its efforts to achieve legitimacy have been tainted by alleged human rights violations.
It also participates in fierce internal conflicts with other groups.
His ambitions beyond Idlib have become unclear.
Since falling out with Al Qaeda, his goal has been limited to trying to establish fundamentalist Islamic rule in Syria instead of a broader caliphate, as the Islamic State has tried and failed to do.
He has shown little sign of trying to revive Syria's wider conflict and renew resistance to Assad's rule over much of the country - until now.
Why is there a war in Syria?
In March 2011, pro-democracy demonstrations broke out in the southern city of Derry, inspired by uprisings in neighboring countries against repressive rulers.
When the Syrian government used lethal force to quell this rebellion, protests broke out across the country demanding the resignation of the president.
Unrest spread, and the suppression of the rebellion became more severe.
Supporters of the opposition took up arms, first to defend themselves, and then to expel the security forces from their own areas.
Assad vowed to suppress what he called "foreign-backed terrorism."
Hundreds of rebel groups emerged, foreign powers began to occupy foreign lands, and extremist jihadist organizations such as Islamic State (IS) In Al Kaida.
The violence rapidly escalated and the country plunged into a full civil war, drawing regional and world powers into it.
More than half a million people died, and 12 million were forced to flee their homes, of which around five million are refugees or asylum seekers abroad.
How did the rebel offensive come about?
For the past four years, the war in Syria has seemed to be practically over.
President Bashar al-Assad's rule was essentially unchallenged in the country's major cities, while some other parts of Syria remained beyond the reach of his direct control.
These included Kurdish-majority areas in the east, which had been more or less separated from Syrian state control since the early days of the conflict.
There has been some ongoing, if relatively subdued, unrest in the south, where the revolution against Assad's rule began in 2011.
In the endless Syrian desert, remnants of the group calling itself Islamic State continue to pose a security threat, especially during the truffle hunting season when people travel to the area to find this highly lucrative delicacy.
In the northwest, the province is held by militant groups that were pushed there at the height of the war.
HTS, the dominant force in Idlib, launched a surprise attack on Aleppo.
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Idlib remained a battleground for several years as Syrian government forces tried to regain control over it.
But the 2020 ceasefire deal brokered by Russia, long a key ally of Assad, and Turska, which supports the rebels, mostly remained in force.
About four million people live there.
Most of them were displaced from towns and cities that Assad's forces retook from rebels in a brutal war of attrition.
Aleppo was one of the bloodiest battlefields and represented one of the biggest defeats of the rebels.
To achieve victory, President Assad could not rely solely on an underequipped and poorly motivated state army of conscripts, which soon became dangerously overstretched and regularly unable to defend positions against insurgent attacks.
Instead, it has come to rely heavily on the Russian air force and the Iranian military for help on the ground – mostly through Tehran-sponsored militias.
Among them was Hezbollah.
There is no doubt that they are a pity Hezbollah recently suffered from the Israeli offensive to Lebanon, just like Israeli strikes on Iranian military commanders in Syria, played a significant role in the decision of jihadists and rebel groups in Idlib to launch this sudden, unexpected movement into Aleppo.
In recent months, Israel has stepped up attacks on groups linked to Iraq, as well as their supply lines, causing serious damage to the networks that have kept these militias, including Hezbollah, operating in Syria.
Without them, President Assad's forces are now left undefended.
Additional reporting: Maya Davis
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