The United States and Israel targeted Iran in coordinated attacks over the weekend that killed Supreme Leader Ayatollah Ali Khamenei and dozens of other senior figures and kicked off a furious Iranian response that was expanding into a wider regional war.

Allies of the U.S. pledged to help stop Iran’s missile and drone strikes. The Lebanese militant group Hezbollah claimed strikes on Israel for the first time in more than a year, and Israel fired back.

The first U.S. military deaths have been reported. Other deaths have been confirmed in Israel and Gulf nations, while Iran has said several hundred people have been killed there.

With Khamenei’s death, the Islamic Republic must now choose a supreme leader for the first time since 1989. U.S. President Donald Trump has urged Iranians to seize the moment and overthrow the theocracy that cracked down on nationwide protests early this year. There was no sign that was happening.

Around the world, some protested. Others cheered.

The attacks came two days after the latest U.S.-Iran talks aimed at putting controls on Tehran’s nuclear program. They echoed the events of last year, when talks were cut short by an Israeli attack that led to a 12-day war and U.S. bombing of Iranian nuclear sites. Washington has claimed that Iran was rebuilding its nuclear program in recent months.

Iran has said it hasn’t enriched since June, but it has blocked inspectors with the U.N. nuclear watchdog from visiting the sites America bombed.

Here’s where things stand.

Iran

The 86-year-old Khamenei was killed when his compound was bombed Saturday morning. Iran’s ballistic missile sites, navy headquarters and warships were attacked as well. Iran said strikes also targeted the Natanz nuclear enrichment site. Israel and the U.S. have not acknowledged strikes at the site, though Israel has said it is targeting the “leadership and nuclear infrastructure.”

Khamenei had no designated successor. Iran has set up a three-member leadership council, and Foreign Minister Abbas Araghchi has said a new supreme leader would be chosen in “one or two days.” On the streets, there have been scattered celebrations over Khamenei’s death. Internet restrictions in Iran have complicated efforts to monitor what’s happening.

In retaliation, Iran’s military has struck Israel, where several people have been killed. Iran has also targeted U.S. bases in the region. The U.S. military said four service members were killed, the first known U.S. casualties. Other Iranian strikes have killed a handful of people in Gulf nations including the United Arab Emirates and Kuwait, and hundreds of flights have been affected at some of the world’s busiest airports.

What to watch for: further military strikes, the selection of a new supreme leader, and reactions from the Iranian people.