The conflict between Iran and Israel is threatening to escalate yet again.

Officials in the United States and Europe believe that Israel appears to be preparing to launch an attack on Iran’s nuclear sites, even as U.S. and Iranian officials engage in talks about curbing Iran’s nuclear program.

Iran’s rulers have pledged to destroy Israel and have long supported regional militias who share that goal. Israel views Iran as an existential threat and has vowed to prevent it from building a nuclear bomb.

In the last year, Israel and Iran have traded airstrikes as their once covert war has burst into the open.

Here is a recent history of the conflict:

2019

Strikes against Iran’s allies

Israel carried out a series of attacks in Syria, Lebanon and Iraq to prevent Iran from equipping its allies with sophisticated weapons. Israel accused Iran of trying to establish an arms supply line through Iraq and northern Syria into Lebanon, where Iran had long backed the militant group Hezbollah.

Israel also attacked ships carrying Iranian oil and weapons through the eastern Mediterranean and Red Seas.

2020

A remote-controlled assassination

In November, Israel killed Iran’s top nuclear scientist, Mohsen Fakhrizadeh, with a remote-controlled machine gun.