(Bloomberg) -- A so-called shadow war between Israel and Iran has shaped the Middle East for decades. Of the many conflicts that have roiled the region, theirs has long been among the most explosive. The two have attacked each other — mostly quietly and in Iran’s case often by proxy — while avoiding an escalation into direct war. But as the fighting between Israel and the Iran-backed Palestinian group Hamas has continued and other militant groups supported by Iran have joined the fray, their conflict has entered a dangerous new phase. On April 13, Iran launched a massive missile and drone attack on Israel, attacking the country for the first time from its own territory. 

Recent Escalation

Iran’s April 13 assault was retaliation for an airstrike two weeks earlier on the country’s diplomatic buildings in the Syrian capital, Damascus, widely attributed to, but not ackowledged by, Israel. The strike killed seven Iranian military personnel, including a top commander of the Islamic Revolutionary Guard Corps, Iran’s premier security force. 

It was just the latest deadly strike in recent months on the Revolutionary Guards in Syria that Iran blamed on Israel. On Jan. 15, Iran used missiles to attack what it said was an Israeli spy base in Iraq in retaliation for a Dec. 25 air strike in Damascus that killed a senior Revolutionary Guard commander. Iran has launched multiple attacks on Kurdistan since late 2022. It accuses separatist Kurdish groups in the region of collaborating with foreign security services against it. Israel has in the past used facilities in northern Iraq to gather intelligence on Iran, according to multiple reports.

From Allies to Enemies 

Israel and Iran were allies starting in the 1950s during the reign of Iran’s last monarch, Shah Mohammad Reza Pahlavi, but the friendship abruptly ended with the Islamic revolution in Iran 1979. The country’s new leaders adopted a strong anti-Israel stance, decrying the Jewish state as an imperialist power in the Middle East. Iran has supported groups that regularly fight Israel, notably Hamas, which the US and European Union consider a terrorist group, and the Hezbollah militia in Lebanon. 

Israel regards Iran’s potential to build nuclear weapons as a threat to its existence and is thought to be behind a campaign of sabotage against the country’s atomic program. Iran’s leaders say they have no ambition to build nuclear weapons. The Israelis point to a cache of documents their intelligence agents spirited out of Iran in 2018 that suggests otherwise. Israeli officials have repeatedly implied that if Iran were to reach the brink of weapons capability, they would attack its nuclear program using air power, as they did Iraq’s in 1981 and Syria’s in 2007.

A Battle of Many Fronts

Lebanon is the oldest front in the battle between Israel and Iran. In reaction to Israel’s invasion of the country’s south in 1982, a militia that would become Hezbollah was formed by Lebanese Muslims belonging to the Shiite branch of Islam dominant in Iran. Their group to some extent became a proxy for the Revolutionary Guards. Israel and Hezbollah have fought repeatedly, including in a war in 2006. Since Oct. 7, Hezbollah has expressed solidarity with Hamas by firing missiles, mortars and rockets into Israel almost daily, prompting Israel to respond with its own fire.

Through the course of Syria’s civil war, Iran has built up a military presence in that country to support its ally, President Bashar al-Assad, and to facilitate the transfer by land of weaponry meant for Hezbollah from Iran to Lebanon via Iraq and Syria. In an effort to stop the arms flow and counter this second hostile presence on its northern border, Israel has carried out hundreds of strikes inside Syria against arms shipments and other targets it says are linked to Iran and its allies, in some cases killing Iranians, according to media accounts. After Oct. 7, Israel stepped up strikes against Iran-backed militias in Syria after they moved close to the Israeli border. 

Another aspect of the shadow war, tit-for-tat attacks on commercial vessels at sea, began in 2019. Although neither Israel nor Iran has accepted responsibility for the hits on ships connected to the other, they are widely thought to be behind them. Loss of life has been rare, but in July 2021, a British and a Romanian crew member were killed when an Israeli-operated ship was struck in the Gulf of Oman by a drone that US officials linked to Iran. Previous targets have included Iranian tankers carrying oil destined for Syria; an Iranian ship off the coast of Yemen that served as a floating base for the Revolutionary Guards; and cargo ships belonging to or linked to Israelis. 

In an escalation of the attacks at sea, since Oct. 7 Iranian-backed Houthi rebels, who’ve controlled northwestern Yemen since civil war broke out in 2014, have attempted to strike Israel with missiles and drones and have repeatedly attacked ships in the Red Sea. The Houthis say they’re targeting vessels linked to Israel — or to the US or UK, which have launched airstrikes on Houthi targets in Yemen in response to the attacks — but ships with no such direction connection have been hit.

Previous Attacks Inside the two Countries

Though Iran in the past had mostly absorbed Israeli strikes on its interests in Syria, in 2018 its forces there fired a barrage of missiles toward Israeli positions in the Golan Heights, a plateau Israel captured from Syria in the 1967 war and later annexed. Israel replied with a much greater show of force. 

For its part, Israel is widely thought to be behind the assassination in Tehran of five Iranian nuclear scientists since 2010 and several attacks on nuclear sites inside Iran. In April 2021, Iran blamed Israel and vowed revenge for an explosion at its largest uranium enrichment facility in Natanz, which it said caused significant damage to its centrifuges. It was the second time in less than a year that the site had been hit by a suspicious blast. Israel neither confirmed nor denied it was responsible for either attack. 

In mid-February, Iran said Israel was behind an attack on its gas transmission network that caused supply disruptions. A year before, after an Iranian ammunition depot near the central city of Isfahan was attacked in a drone strike, two US newspapers reported that Israel was responsible. In 2021, an Iranian general said Israel was likely behind a cyberattack that paralyzed gas stations across Iran. 

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