By Cassandra Vinograd

Published Jan. 18, 2024

Updated Jan. 19, 2024, 9:33 a.m. ET

Israel and Gaza. Yemen and the Red Sea. Lebanon, Syria, Iraq — and now Pakistan, too.

At every flashpoint in a set of conflicts spanning 1,800 miles and involving a hodgepodge of unpredictable armed actors and interests, there’s been a common thread: Iran. Tehran has left its imprint with its behind-the-scenes backing of combatants in places like Lebanon and Yemen, and with this week’s direct missile strikes on targets in Iraq, Syria and Pakistan.

The Iran connection stems partly from Iran’s decades-long efforts to deter threats and undermine foes by building up like-minded militias across the Middle East.

In addition, Iran itself, like neighboring countries, faces armed separatist movements and terrorist groups in conflicts that readily spill over borders.

But what does Pakistan have to do with Gaza? Here’s a look at how Iran ties together recent tensions.

What’s the back story here?

Ever since the 1979 revolution that made Iran a Shiite Muslim theocracy, it has been isolated and has seen itself as besieged.

Iran considers the United States and Israel to be its biggest enemies — for more than four decades its leaders have vowed to destroy Israel. It also wants to establish itself as the most powerful nation in the Persian Gulf region, where its chief rival is Saudi Arabia, an American ally, and has often had hostile relations with the Saudis and some other predominantly Sunni Muslim Arab neighbors.

With few other allies, Iran has long armed, trained, financed, advised and even directed several movements that share Iran’s enemies. Though Iranian forces have been involved directly in wars in Syria and Iraq, Tehran has mostly fought its enemies abroad by proxy.

Iran, which calls itself and these militias the “Axis of Resistance” to American and Israeli power, sees it all as “part of a single struggle,” said Hasan Alhasan, a senior fellow for Middle East Policy at the International Institute for Strategic Studies, a policy analysis group.

Iranian leaders call their approach a forward defense strategy, saying that to defend itself, the country must take action outside its borders.

“If they are to avoid fighting the Americans and Israelis on Iran’s soil, they’ll have to do it elsewhere,” Mr. Alhasan said. “And that’s in Iraq, Syria, Yemen, Palestine, Afghanistan.”

How well the strategy works is open to question. Terrorist groups have attacked recently on Iranian soil. And for years Israel has carried out targeted attacks on Iran’s nuclear program, killing some of its key figures and destroying facilities.

Why does Iran outsource its conflicts?

While Iran wants to project its power and influence, it is reluctant to directly engage the United States or its allies, courting major retaliation or all-out war.

How secure Iran’s leaders feel in their grip on power is unclear. But they know that decades of sanctions and embargoes have degraded Iran’s military forces and its economy, and that their repressive government faces intense domestic opposition.

Iran has hoped to compensate for its vulnerabilities by raising the prospect that it could develop nuclear weapons — which would put it on par with Pakistan and Israel, and ahead of Saudi Arabia.

Iran maintains that its nuclear program has only peaceful purposes, and Tehran has carefully kept the uranium it produces just below the threshold for bomb-grade fuel, which is considered the red line that could trigger military action against its underground nuclear complexes.

Investing in proxy forces — fellow Shiites in Lebanon, Iraq and Yemen, and the Sunni Hamas in the Gaza Strip — allows Iran to cause trouble for its enemies, and to raise the prospect of causing more if attacked.

“Proxy forces have allowed Iran to maintain some level of plausible deniability, while asymmetrically supplying Tehran with a means to effectively strike Israel or apply pressure to it,” the Combating Terrorism Center at West Point wrote in a December report.

Iranian officials have publicly denied being involved in or ordering Hamas’s Oct. 7 attack on Israel that killed about 1,200 people. But they also praised the assault as a momentous achievement, and warned that their regional network would open multiple fronts against Israel if the country kept up its retaliatory war against Hamas in Gaza.

Some of those proxies have, in fact, stepped up attacks on Israel, but have avoided full-fledged warfare.

People waving yellow-and-green Hezbollah banners watch the group’s leader, Sayyed Hassan Nasrallah, deliver a speech on a giant video screen.

Who are these proxies for Iran?

Hezbollah in Lebanon, widely considered to be the most powerful and sophisticated of the Iran-allied forces, was founded in the 1980s with Iranian assistance, specifically to fight the Israeli occupation of southern Lebanon. The group, which is also a political party in Lebanon, has fought multiple wars and border skirmishes with Israel.

Hezbollah has been trading fire across the border with Israel’s military almost daily since the Oct. 7 Hamas-led attacks, but it has thus far refrained from fully joining the fight.

The Houthi movement in Yemen launched an insurgency against the government two decades ago. What was once a ragtag rebel force gained power thanks at least in part to covert military aid from Iran, according to American and Middle Eastern officials and analysts.

The Houthis seized much of the country in 2014 and 2015, and a Saudi-led coalition stepped into the civil war on the side of the Yemeni government. A de facto cease-fire has held since 2022, with the Houthis still in control of Yemen’s northwest and its capital, Sana.

Since the war in Gaza began, the Houthis have waged what they call a campaign in solidarity with Palestinians under Israeli bombardment. They have launched missiles and drones at Israel, and have disrupted a significant part of the world’s shipping by attacking dozens of vessels heading to or from the Suez Canal.

That has transformed the Houthis into a force with a global impact, and prompted the United States and Britain, with help from allies, to carry out missile strikes on Houthi targets inside Yemen.

Hamas, in the Palestinian territories, has also received weapons and training from Iran, and has fought repeated wars with Israel.

Why did Iran strike directly, not through allies, in Iraq, Syria and Pakistan?

It has a lot to do with the government’s problems at home.

As tensions rise across the region, Tehran has increasingly become a target.

Last month, a separatist group attacked a police station in southeastern Iran, killing 11 people. Two senior Iranian commanders were assassinated in Syria, and Iran blamed Israel.

Then this month, suicide bombings in Kerman, Iran, killed almost 100 people — the deadliest terrorist attacks since the Islamic Republic was founded. The Islamic State claimed responsibility.

Iran analysts, and Iranians close to the military, say the government wanted to make a show of force with an eye to the hard-liners who make up its base of support, and were already incensed at Israeli attacks. Iran went on the offensive.

It said this week that it had fired missiles at the Islamic State in Syria, and at what it said was an Israeli base for intelligence gathering in northern Iraq. (The Iraqi government denied that the building struck was tied to Israel.) It also fired into Pakistan.

“Iran has signalled clearly that it is not willing to deploy those capabilities for anything less than the defence of their homeland,” said Ali Vaez, the Iran project director at the International Crisis Group, a policy group.

What does Pakistan have to do with this? It’s not even in the Middle East.

The separatist group Jaish al-Adl wants to create a homeland for the Baluch ethnic group out of parts of Iran and Pakistan, and it operates on both sides of the border. It also took responsibility for the deadly attack last month on an Iranian police station.

The two countries have accused each other of not doing enough to prevent militants from crossing the border.

Iran said its strikes in Pakistan targeted bases for Jaish al-Adl, but Pakistan pushed back against Iran’s reasoning, citing what it said were civilian casualties. On Thursday, Pakistan responded by bombing what it said were terrorist hide-outs inside Iran.

Pakistan and Iran have had mostly cordial relations, and the frictions between them have little to do with Iran’s other regional conflicts. But Iran’s decision to strike inside Pakistan has the potential to damage its relationship with Pakistan. At a time when the region is already on edge, a miscalculation could be especially dangerous.

Vivian Nereim, Salman Masood and Farnaz Fassihi contributed reporting.

A correction was made on Jan. 19, 2024: An earlier version of this article referred incorrectly to Iran’s nuclear program. Iran has raised the prospect that it could develop nuclear weapons, maintaining that its nuclear program has only peaceful purposes, but it has not developed them.

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A version of this article appears in print on Jan. 19, 2024, Section A, Page 6 of the New York edition with the headline: Why Iran Is the Common Link in a String of Conflicts, From Gaza to Pakistan. Order Reprints | Today’s Paper | Subscribe