Renewed fighting in the Syrian civil war, which has killed more than 300,000 people and driven nearly 6 million refugees from the country since 2011, will have far-reaching effects across the Middle East and beyond.

Here is what you need to know If you catch up on the conflict:

What happened in the Syrian civil war? At the height of the Arab Spring in 2011, pro-democracy protesters took to the streets in Syria, demanding the overthrow of authoritarian President Bashar al-Assad. The protesters were met with lethal force. As Assad’s forces crushed the democracy movement, an armed opposition began to form, consisting of small organic militias and some defectors from the Syrian military.

Support for the opposition forces: The opposition forces – which are decentralized and made up of different ideologies but share a common goal of toppling Assad – have been supported in various ways by foreign powers, including neighboring Turkey, regional giants Saudi Arabia and the United Arab Emirates, as well as the United States.

Assad’s allies: As anti-government forces grew, Syria’s allies Iran and Russia increased their support. On site, Iran’s Islamic Revolutionary Guard Corps and its Lebanese proxy Hezbollah helped fight the armed rebel groups. In the air, the Syrian Air Force was reinforced by Russian fighter jets.

ISIS gets involved: In 2014, extremist groups within the opposition coalition outnumbered moderate groups, and ISIS spread across the country. Fearing that Syria would become a permanent source of terror, a US-led international coalition intervened with the aim of eliminating the group without confronting the Syrian regime. The Syrian Democratic Forces (SDF) – a US partner made up of Kurdish fighters – fought against ISIS, effectively ending the group’s territorial existence.

The last big development: In 2020, Russia and Turkey agreed to a ceasefire in their proxy war over the last remaining opposition-controlled province of Idlib. There have been no major outbreaks since then, but the Syrian government has never retaken all of its territory. And as the events in Aleppo show, armed resistance never completely disappeared.

Why has the conflict flared up again now?: The offensive began after rebels formed a new coalition called the Military Operations Command. They quickly swept through villages outside Aleppo, and residents now said they controlled much of the city, encountering little resistance along the way. The fighters say they sought to liberate occupied territories and responded to increasing attacks by government troops and pro-Iranian militia groups.

CNN’s Eyad Kourdi, Ben Wedeman, Mostafa Salem and Christian Edwards contributed to this report.