The Nasrallah killing is upending Iran’s security strategy. Here’s what to expect next.

The Iranian attack against Israel on October 1 did not take place in a void. It was strongly connected to the significant Israeli military success against Hezbollah in Lebanon and the failure of Iranian proxies to force Israel to stop the war against Hamas in the Gaza Strip.

To better understand the origins of this attack, one must return to the Iranian proxy strategy, developed and perfected by Islamic Revolutionary Guard Corps (IRGC) Quds Force commander Qasem Soleimani—who, until his assassination in 2020, was considered one of the most sophisticated strategists of the Islamic Republic of Iran. Iran’s ability to establish, maintain, and arm terrorist organizations that are physically close to Israel allowed Tehran to dramatically increase its deterrence against the “Zionist entity” without paying a real price.

Moreover, these proxies allowed Iran to do what it needed the most: keep the wars away from its borders. The current Iranian leadership, including Supreme Leader Ayatollah Ali Khamenei—who was shaped by the eight-year Iran-Iraq war—is worried that Iran will be forced to defend its borders in a way that could potentially threaten the future of the regime. The proxies became part of Iran’s strategic depth policy, which allowed Tehran to engage its enemies without fear that these conflicts would spill over into Iran.

Among the affiliates that Iran has been able to develop over the years, the most significant and powerful organization is, of course, Hezbollah. The group in Lebanon has grown stronger over the years not only politically—due to the decision of the organization’s late Secretary-General Hassan Nasrallah—but mainly militarily, through the generous and powerful assistance of Tehran, which transformed Hezbollah from a terrorist organization into a terrorist army.

In practice, the Iranian and Syrian military industries gave Hezbollah advanced capabilities that allowed it to threaten Israel. In this sense, the organization has become a significant Iranian deterrent tool when Israel considers attacking Iran’s nuclear facilities.

The Hezbollah organization, along with other proxies in the Middle East—like the Shia militias in Iraq and the Houthis in Yemen—promoted and developed their military capabilities. The groups’ strategic capabilities also deepened Iran’s understanding that they create a significant deterrent against Israel and have become a central component of Iran’s national security.

Moreover, paradoxically, Iran’s attack on Israel on April 13 might have sharpened Tehran’s understanding of the importance of Hezbollah. Iran’s operational failure in this attack—together with Israel’s interception of Iranian missiles and the deep involvement of the Sunni Arab countries in Israel’s efforts to thwart this attack—led to minor damage in Israel. For Iran, this result probably emphasized the importance of Hezbollah for Iranian security, with an emphasis on the group’s ability to cause significant damage to Israel using the existing means at its disposal. However, Hezbollah’s reaction against Israel’s unprecedented moves against the organization, which culminated in the death of Nasrallah on September 27 and the communications attacks earlier in the month, made it clear to the leadership in Tehran that future reliance on the Resistance Axis as a deterrent against Israel is not possible. Thus, despite all of Iran’s investment, Hezbollah’s weakness emphasizes the gap between the threats voiced by Nasrallah and the actual implementation.

Furthermore, in light of the deaths of Nasrallah and IRGC Deputy Commander Abbas Nilforoushan, Hassan Mahdawi‘s replacement as commander of the Quds Force in Lebanon, Tehran had to decide what would strengthen its deterrence against Israel directly when it seems that Israel is dramatically restoring its ability to project power in the region. It is important to note that, after the April 13 attack, Iran thought that it had rebalanced the deterrence equation vis-à-vis Israel through its unprecedented response to the assassination of Mahdawi. On the other hand, after the assassination of Hamas political chief Ismail Haniyeh in Tehran in July, which it attributed to Israel, Iran was cautious not to react directly against Israel despite the threats of its leadership.

After intense deliberation about how to reset the deterrence equation with Israel after the elimination of Nasrallah and Nilforushan, Iran decided to attack Israel with almost two hundred ballistic missiles aimed at air force and other military bases. It seems that the clerical establishment took this complex decision while understanding that attacking Israel is the only way to rebuild the deterrence equation while highlighting to Resistance Axis members that Iran supports them and might hamper the Israeli attack against Hezbollah. Iran took a considerable risk because, unlike in the April 13 retaliation, Hezbollah cannot join Iran in any future attack against Israel and the United States probably won’t prevent an Israeli attack. Khamenei probably felt that he had no other choice, and Iran would need to build its deterrence with Israel independently.

Regardless of how the current escalation against Israel ends, Iran will need to rethink its national security strategy and take these possible steps. It is clear that, first and foremost, Iran will try to rehabilitate the Hezbollah organization through massive military transfers, sending various elements on behalf of Iran to stabilize the leadership of the organization and, of course, support Nasrallah’s replacement (likely Hashem Safieddine, though he might have been killed in a strike on October 3). To do that, Iran will need to preserve its influence on Syrian President Bashar al-Assad and its presence within Syria, which, given its geographical location, is a vital component in Iran’s efforts to transfer arms to Hezbollah.

Iran hopes that it will be possible, even in the current round of escalation, to exact a significant price from Israel to avoid a situation in which Israel does everything it can against Hezbollah. Iran will do this by reorganizing Hezbollah’s structure, rebuilding its command-and-control capabilities, and, perhaps, by using IRGC personnel in Lebanon and Syria.  

At the same time, Iran will probably try to examine whether it is possible to strengthen the capabilities of the Shia militias in Iraq and the Houthis in Yemen, as well as to increase the transfers of explosives to the West Bank, while trying to rebuild Hamas military capabilities in Gaza by using its renewed cooperation with the Sudanese army. It will also probably try to undermine Jordan’s security while trying to open another front against Israel from Amman. This might compensate for the dramatic damage that Hezbollah suffered in the war with Israel.

In addition, Iran will seek to use its close relationship with Russia to increase its military capabilities dramatically. Iran is about to complete its Sukhoi Su-35 deal and will receive advanced air-defense capabilities such as the S-400 to improve its defense capabilities (if it doesn’t already have them). It is quite clear that Iran—which relies mainly on its missile and unmanned aerial vehicle (UAV) capabilities—will attempt, in cooperation with the Russians and countries such as North Korea, to significantly upgrade these capabilities, with an emphasis on improving their accuracy, upgrading their quantity, and extending their range to allow Iran to increase the direct threat to Israel. In addition, Iran will likely increase threats to its Arab neighbors and warn them that it will not hesitate to attack those that cooperate with any Israeli military action against Iran. Iran will also increase its public military exercises and deepen its intelligence cooperation with Russia to identify the possibility of an attack by Israel. It cannot be ruled out that Iran will ask to send forces outside its borders to increase the projection of its power, including in the maritime domain.

Above all, there is the nuclear question. Iran today is very close to 90 percent enrichment; even US Secretary of State Antony Blinken admitted that. But according to the best estimates, it is still many months away from being able to build a nuclear weapon. Without Hezbollah, when Israel’s actions demonstrate its capabilities and intentions, the question of nuclear deterrence will likely be put to the test again. Various officials in Iran have already expressed themselves in this regard. Iran can try to advance on the military path or—in line with the wishes of Iranian President Masoud Pezeshkian—could quickly strive for a nuclear deal that will take the sting out of the Israeli threats and significantly reduce the likelihood that someone will support an Israeli attack on Iran’s nuclear sites.

As an intermediate step, Iran can—as it did during its tensions with Israel in April—return to using its proximity to weapons-grade enrichment as a tool to deter Israel, including the possibility of crossing the Rubicon as a symbolic step but one that demonstrates its capabilities. As the escalation with Israel continues, the chances that Iran will enrich to 90 percent are becoming higher. Iran may feel that its nuclear sites are in danger or that its conventional means are not sufficient to deter Israel—there are already voices in the regime calling for enriching to 90 percent.

Iran will need to think carefully about whether it is suitable to create another direct confrontation with Israel, which might also lead it to a direct confrontation with the United States. However, it can potentially balance the deterrence equation vis-à-vis Israel by pursuing a nuclear deal that will end the current escalation and reduce the risks of direct confrontation with Israel, creating a possible wedge between the United States and Israel and buying Iran time to think about its national security. If Iran decides to go down this path, it must consider that there will be a new US administration in January, which presumably will continue to support Israel but, on the other hand, might be interested in a deal to prevent a regional war.

Iran’s decision regarding the ceasefire will also testify to Iranian policy in this context. Tehran needs to decide whether it is ready to change its policy since October 7, 2023. This would, in effect, give up on Hamas in the Gaza Strip and pursue a deal that separates what is happening in Gaza from what is happening in Lebanon—thus saving Hezbollah at the expense of Hamas—or continuing without any change, similar to Nasrallah’s approach and, therefore, endangering Iran in a regional campaign.

The bottom line is that the consequences of the dramatic damage to Hezbollah and the elimination of Nasrallah go far beyond the issue of the proxy group. The latest events, particularly the attack on Israel on October 1, could lead to a profound change in Iran’s national security and increase the likelihood of a confrontation between Israel and Iran.

Danny Citrinowicz is a nonresident fellow with the Atlantic Council’s Middle East Programs and a fellow at the Institute for National Security Studies. Follow him on X: @citrinowicz.

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Image: People walk next to the stands with the flags of Iran, Hezbollah and Lebanon in a street in Tehran, Iran, October 7, 2024. Majid Asgaripour/WANA (West Asia News Agency) via REUTERS