The 13-year civil war in Syria has roared back into prominence with a surprise rebel offensive during which they seized Aleppo, one of Syria’s largest cities and an ancient business hub. The push is among the rebels’ strongest in years in a war whose destabilizing effects have rippled far beyond the country’s borders. It was the first opposition attack on Aleppo since 2016, when a brutal air campaign by Russian warplanes helped Syrian President Bashar Assad retake the northwestern city. Intervention by Russia, Iran and Iranian-allied Hezbollah and other groups had allowed Assad to remain in power within the 70% of Syria under his control. Insurgents led by jihadi group Hayat Tahrir al-Sham launched the two-pronged attack on Aleppo last week and moved into the countryside around Idlib and neighboring Hama province. The Syrian military has rushed reinforcements and launched airstrikes as they attempted to stall their momentum. The surge in fighting has raised the prospect of another violent front reopening in the Middle East, at a time when U.S.-backed Israel is fighting Hamas in Gaza and Hezbollah in Lebanon, both Iranian-allied groups. Robert Ford, the last-serving U.S. ambassador to Syria, pointed to months of Israeli strikes on Syrian and Hezbollah targets in the area, and to Israel’s ceasefire with Hezbollah in Lebanon last week, as factors providing Syria’s rebels with the opportunity to advance. Russia, Assad’s main international backer, is also preoccupied with its war in Ukraine. Here’s a look at some of the key aspects of the new fighting: Why does the fighting in Aleppo matter? Assad has been at war with opposition forces seeking his overthrow for 13 years, a conflict that’s killed an estimated half-million people. The conflict started as one of the Arab Spring popular uprisings in 2011 against Arab dictators, before Assad’s brutal response to what had been largely peaceful protests turned the conflict violent. Some 6.8 million Syrians have fled the country since then, a refugee flow that helped change the political map in Europe by fueling anti-immigrant far-right movements. The roughly 30% of the country not under Assad is controlled by a range of opposition forces and foreign troops. The U.S. has about 900 troops in northeast Syria, far from Aleppo, to guard against a resurgence by the Islamic State. Both the U.S. and Israel conduct occasional strikes in Syria against government forces and Iran-allied militias. Turkey has forces in Syria as well, and has influence with the broad alliance of opposition forces storming Aleppo. Coming after years with few sizeable changes in territory between Syria’s warring parties, the fighting “has the potential to be really quite, quite consequential and potentially game-changing,” if Syrian government forces prove unable to hold their ground, said Charles Lister, a longtime Syria analyst with the U.S.-based Middle East Institute. Risks include if militants with the Islamic State extremist group see the renewed fighting as an opening, Lister said. The Islamic State, a violently anti-Western and repressive organization, in 2014 notoriously declared a self-styled caliphate that seized parts of Syria and Iraq. The Islamic State’s Syria and Iraq branch no longer controls any territory, and is not known to be playing a role in the current fighting. But is still a lethal force operating through sleeper cells in the two countries. Ford said the fighting in Aleppo would become more broadly […]