Hezbollah is an Iranian-backed Islamist movement with one of the most powerful paramilitary forces in the Middle East. The group’s main base is on the border between Israel and Lebanon, where the fallout from the war between Israel and Hamas has been felt. Hezbollah and Israel have been locked in skirmishes since the war began, putting the entire region on edge with fears that it could spark a wider regional conflict.

This is the latest in a decades-long conflict between Hezbollah and Israel. Here’s what you need to know:

Israeli invasion: Israeli forces seized nearly half of Lebanon’s territory when it invaded Lebanon in 1982. This included Beirut, where Israeli forces, along with right-wing Christian Lebanese militias allied with Israel, besieged the western part of the capital to drive out Palestinian militants.

The Israeli operation resulted in more than 17,000 deaths, according to contemporary reports and an Israeli investigation into a massacre in the Sabra and Shatila refugee camp in Beirut. It is one of the bloodiest events in the region’s recent history. The investigation, known as the Kahan Commission of Inquiry, held Israel indirectly responsible for the massacre, which was carried out by right-wing Lebanese Christian militants. Estimates of the number of deaths in Sabra and Shatila vary between 700 and 3,000.

The Rise of Hezbollah: As Palestinian fighters poured out of Lebanon, a group of Shiite Islamist fighters, trained by the emerging Islamic Republic of Iran, burst onto Lebanon’s divided political landscape. The motley crew had an outrageous and violent impact. In 1983, two suicide bombers linked to the faction attacked a U.S. Marine barracks in Beirut, killing nearly 300 American and French personnel, plus several civilians.

A year later, Iran-linked fighters bombed the U.S. embassy in Beirut, killing 23 people. In 1985, these militants united more formally around a newly formed organization: Hezbollah.

A ‘supportive front’ for Gaza in 2023: Hezbollah is part of a larger Iran-led alliance of militant groups spanning Yemen, Syria, Gaza and Iraq that has increasingly clashed with Israel and its allies since the war with Hamas began on October 7, 2023. The alliance has said it will continue to strike Israeli targets as long as the war in Gaza continues, and has described itself as a “support front” for Palestinians in the Strip, as described by a senior Hezbollah leader.

Assassination of important leader: After months of tit-for-tat exchanges, tensions escalated when Israel said it had killed Hezbollah’s top military commander, Fu’ad Shukr, in a strike on Beirut in July. In retaliation, Hezbollah launched hundreds of drones and missiles at targets in Israel in August. Israel has denied that any significant targets were hit, and no evidence has been made public to contradict that denial.

Displaced residents: The increase in cross-border fighting has forced people to flee their homes in both northern Israel and southern Lebanon. On Tuesday, Israel made it a new war goal to send tens of thousands of northern Israelis back to their homes near the border. Officials and residents of the northern region have increasingly pressured the Israeli government on the need for the return. More than 100,000 people have been displaced from southern Lebanon, according to Lebanon’s Health Ministry.

Final attack: Hezbollah confirmed that senior commander Ibrahim Aqil was killed on Friday. Israel said Aqil was among senior Hezbollah figures killed in an airstrike on a residential building in Beirut. Lebanon was already reeling after thousands of small explosions hit Hezbollah members’ pagers and walkie-talkies throughout the week, killing dozens and wounding thousands.