Tel Aviv. Israel’s massive strike on Iran on Friday morning came after decades of hostilities between the bitter enemies.

Israeli Prime Minister Benjamin Netanyahu has long identified Iran as its greatest threat, citing the country’s nuclear program, its hostile rhetoric and support for anti-Israel proxy groups across the region. Iran meanwhile, has pointed to Israel's repeated assassination and sabotage attacks targeting it, as well as its devastating war on Hamas in the Gaza Strip, for its enmity.

While the two countries have long appeared to be on a collision course, a series of recent developments, including Israeli blows against Iran and its allies and the re-election of President Donald Trump, helped lay the groundwork for Friday’s attack.

Here’s a closer look:

Why Are Israel and Iran Enemies?
Following Iran’s 1979 Islamic Revolution, the country’s leadership immediately identified the United States and Israel as its main enemies. This was connected in large part to American and Israeli ties to Iran’s last shah, Mohammad Reza Pahlavi, who fled Iran while fatally ill ahead of the revolution and despised by Iran's new leaders.

Over the past two decades, Israel has repeatedly accused Iran of developing nuclear weapons. Iran insists it has maintained its nuclear program for peaceful purposes only, but the head of the UN atomic watchdog agency has warned that Tehran has enough uranium enriched to near-weapons-grade levels to make “several” nuclear bombs if it chose to do so.

The International Atomic Energy Agency and Western nations assessed that Iran had an organized nuclear weapons program until 2003. Iran insists its program is peaceful while still enriching uranium to near weapons-grade levels. US intelligence agencies have assessed that Iran was not pursuing the bomb.

Israel sees a nuclear-armed Iran as an existential threat, and breaking Iran’s regional network of militant proxy groups has been a major goal.

“For decades, the tyrants of Tehran have brazenly, openly called for Israel’s destruction,” Netanyahu said Friday. “They backed up their genocidal rhetoric with a program to develop nuclear weapons.”

As he has done before, Netanyahu drew comparisons to the Holocaust. “The Jewish state refuses to be a victim of a nuclear Holocaust perpetrated by the Iranian regime,” he said.

Iran's Axis of Resistance Has Been Weakened
Over the past four decades, Iran built up a network of militant proxy groups it called the “Axis of Resistance.” These groups -- Hamas in Gaza, Hezbollah in Lebanon, the Houthis in Yemen, and smaller militias in Iraq and Syria -- wielded significant power across the region in recent years.

But the axis has weakened since Hamas attacked Israel on Oct. 7, 2023, triggering the ongoing war in Gaza and wider fighting across the region.

Israel has decimated Iran’s strongest proxies, Hamas and Hezbollah. The weakening of Hezbollah contributed to the downfall of Iran’s longtime stalwart ally and client in neighboring Syria, President Bashar Assad, last December.

After Iran launched a pair of missile attacks on Israel last year, Israel responded with strikes of its own, including an October attack that destroyed Iranian missile sites and weakened its air defenses.

The collapse of Iran’s proxy network, coupled with Iran's new vulnerability, created an opportunity for Israel to strike.

Why Did Israel Decide to Strike Now?
Netanyahu said time was running out to strike Iran, alleging Iran had taken recent steps to weaponize enriched uranium. “If not stopped, Iran could produce a nuclear weapon within a very short time,” he said.

At the same time, the state of nuclear talks between the US and Iran created a window. Those talks have been faltering, but a sixth round was scheduled for Oman on Sunday.

An agreement could see the US lift some of its crushing economic sanctions on Iran and make it much harder for Israel to strike. Israeli officials feared the talks were a way for Iran to buy time as it secretly took steps toward a nuclear bomb.

On Thursday, for the first time in 20 years, the Board of Governors at the IAEA censured Iran for not working with its inspectors. Iran immediately announced it would establish a third enrichment site and swap out some centrifuges for more advanced ones.

By then, Israel apparently had already made up its mind.

Trump said he asked Netanyahu not to attack Iran while the negotiations are ongoing. But Trump has a long record of support for Israel, and there appeared to be little immediate blowback.