Defending the Assad regime has given Tehran multiple options for expanding its influence and projecting power in the region and beyond.

The Syrian civil war is transforming regional geopolitics, and one of its most dramatic effects is Iran's seemingly expanding foothold in the Eastern Mediterranean and the Levant. While it is too early to know the ultimate implications of this development, several potential consequences have become clear.

AN EVOLVING INTERVENTION

When "Arab Spring" protests first broke out in Syria, Tehran reportedly supplied the Assad regime with crowd-control gear and Internet surveillance technology, as well as advice on how to handle demonstrations, based on its own success in quashing the Green Movement in 2009. By 2012, however, the regime's violent response to peaceful protests had spawned a bloody civil war that it was losing. Accordingly, Iran pressed Hezbollah to join the fight and deployed personnel from the Islamic Revolutionary Guard Corps-Qods Force to advise the Syrians -- though some were involved in combat almost from the start. Tehran also oversaw the deployment of Iraqi (2012), Afghan (2013), and Pakistani (2014) Shiite militiamen to Syria.

Meanwhile, Iran reorganized the Assad regime's armed shabbiha and Popular Committees into a militia of about 100,000-150,000 fighters known as the National Defense Forces (NDF), modeled after the Islamic Republic's own paramilitary Basij. Iranian IRGC officers are believed to direct the operations of the NDF, which has come to rival, if not overshadow, the Syrian Arab Army (SAA).

More recently, Iran deployed hundreds of regular IRGC personnel to augment Hezbollah and Syrian forces. Its total number of personnel there is unclear, however -- estimates range from the high hundreds to the low thousands, augmenting 4,000-5,000 Hezbollah fighters and many thousand other Shiite militiamen.

Since acknowledging its first combat fatality in February 2013, Iran has admitted to losing about 140 IRGC members in Syria, indicating that its personnel are actively involved in combat (see PolicyWatch 2458, "Shiite Combat Casualties Show the Depth of Iran's Involvement in Syria"). Tehran has probably sent a significant slice of the IRGC-QF to Syria, including some of its most senior personnel; indeed, several Qods Force generals have been killed in combat. By contrast, it has sent a relatively small slice of its 100,000-man regular IRGC ground forces, preferring to use Shiite militia proxies as cannon fodder (more Afghan militiamen have been killed in Syria than Iranians), to limit its exposure and defray the human cost of its intervention.

Tehran has laid the foundation for long-term influence not only by remaking the Syrian security sector in its image, but also by providing billions of dollars in cash and oil to the regime while burrowing into Syria's civil society and economy. Iranian entities are reportedly buying up properties, setting up businesses, bidding on government contracts, and bolstering trade to create a web of dependency. Iranian authorities have also tried their hand at demographic engineering, (unsuccessfully) negotiating local ceasefires and population swaps around Zabadani and the Shiite villages of al-Fua and Kefraya. In short, Tehran appears to be using the same playbook it employed to gain influence in Iraq last decade (see Policy Focus 111, Iran's Influence in Iraq: Countering Tehran's Whole-of-Government Approach).

The recent Russian intervention may complicate matters for Iran, however. If Tehran had gone all-in with more ground forces earlier in the war, the Assad regime might not have needed Moscow's help. Instead, Iran is no longer Syria's sole patron -- it is waging coalition warfare now, and Russia will have a major say in how the conflict is prosecuted. Some Syrians resent Iran's role and would welcome the return of Russian influence at Tehran's expense. So far, though, Iran and Moscow seem to be reading from the same script.

In sum, Tehran has derived a number of benefits from its military and financial assistance to Syria. By intervening in 2012, it saved its sole ally in the region, preserved the air bridge to its Hezbollah proxy in Lebanon, and established itself as an ally that can be relied on when the chips are down. And when its own capabilities proved insufficient, Iran apparently lobbied Russia to intervene, further proving its commitment. Conversely, Syria has effectively been transformed from an ally of Iran and Hezbollah to an indebted client state. Whether Russia joins them as an equal or a senior partner remains to be seen. Whatever the case, Iran's role in the war has a number of potential long-term implications for the region.

INTENSIFIED SECTARIAN CONFLICT

Tehran's intervention has been the driving force behind the Middle East's increased sectarian polarization in recent years, as well as the unprecedented jihadist mobilization (Sunni and Shiite) for the Syria fight. These developments enabled Tehran to rally much of the region's 20 percent Shiite population to its side, but at the cost of convincing the 75 percent Sunni Arab population that Iran is a grave threat to their identity and interests. Such fears have united previously irreconcilable states -- Turkey, Saudi Arabia, Qatar -- in a Sunni axis and helped spur the Saudi-led intervention in Yemen. The legacy of these developments will shape regional politics and demography for decades to come.

EXPANDED "AXIS OF RESISTANCE"

Iran's advisory and combat presence in Syria has dramatically increased its range of contacts there, including a broader cross-section of the SAA and NDF. It has also mobilized a transnational network of Shiite militias that effectively serve as Iran's "Foreign Legion," countering the Sunni networks of ISIS and al-Qaeda. This network will provide an external base of support for Iranian policies from Lebanon to Pakistan, and the assets unfrozen by the P5+1 nuclear deal may further Tehran's efforts to recruit, maintain, and consolidate it.

FORCE PROJECTION IN THE EASTERN MEDITERRANEAN?

Iran could eventually exploit its Levantine foothold to create an antiaccess "bubble" along the Lebanese and Syrian coasts, using the more capable Russian bubble around Tartus and Latakia to shield its own effort. To some extent, this would depend on Iran and Syria's ability to transfer advanced antiship and antiaircraft weapons to Hezbollah, despite Israeli efforts to interdict such transfers. The two might also work together to create a rudimentary reconnaissance-strike complex in the Eastern Mediterranean to threaten Israel's critical coastal infrastructure (power stations and ports) and offshore assets (natural gas platforms), as well as the seaborne leg of NATO's missile defense (see PolicyWatch 1722, "Potential Iranian Responses to NATO's Missile Defense Shield").

A FORWARD MISSILE BASE?

Tehran may seek to enhance the range and striking power of its rocket and missile forces by deploying some of them in Syria. (This would not be unprecedented; both the United States and the Soviet Union deployed missiles overseas during the Cold War.) Iran has a very large inventory of long-range rockets, and perhaps a thousand short- and medium-range ballistic missiles. At present, only around half of these missiles (with claimed ranges of up to 2,000 kilometers) can reach Israel. None of the rockets (some with claimed ranges of 500 kilometers) have that capability. But if Iran deployed large numbers of them to Syria, it could overwhelm Israeli missile defenses, giving Tehran an independent option if circumstances prevent Hezbollah from using its own rockets against Israel in a future crisis. Deploying medium-range ballistic missiles to Syria would also bring Central Europe within Iran's range. At the same time, Tehran might replenish the Assad regime's depleted missile stocks to give it an independent retaliatory capability.

NEW FRONTS AGAINST ISRAEL AND JORDAN

For some time now, Hezbollah and the IRGC-QF have been trying to establish a presence in the northern portion of the Syrian Golan Heights in order to create a new front for proxy action against Israel. To this end, they have stood up a Druze militia in the town of Hader. In February, Iranian officers apparently directed a failed offensive to retake the Syrian Golan from rebel forces using SAA, NDF, Hezbollah, and Shiite militia forces. These efforts are certain to continue. Iran may also try to establish a presence along the Jordanian border for several reasons: to pressure Amman into halting its support for rebels in southern Syria, to destabilize a key Israeli and U.S. ally, and to act on Supreme Leader Ali Khamenei's stated desire to arm Palestinians in the West Bank (a difficult prospect).

REBALANCING PRO-REGIME FORCES?

Thus far, Russian support has apparently reinvigorated the SAA, and the pro-regime coalition seems to be working together in an integrated fashion. Russia's experience with employing conventional forces alongside militias and irregulars in Ukraine may make it amenable to the hybrid approach preferred by Syria, Iran, and Hezbollah. Yet the long-term effects of Russian assistance remain to be seen. Will Moscow and Tehran establish a division of labor, effectively creating spheres of influence among coalition forces -- with Russia assisting the SAA, and Iran the NDF and foreign Shiite militias? Or will Moscow insist on a preeminent role and seek to rebalance the coalition, perhaps helping the SAA reemerge as the country's strongest military force (an option many Syrian officers might prefer)? If so, what impact might this have on the Assad regime's internal politics, its relationship with Iran, and Tehran's equities in Syria?

ENHANCED MILITARY CAPABILITIES

Even if Iran's cooperation with Russia is limited, interacting with a military superpower may enable it to learn key lessons and pick up advanced tactics, techniques, and procedures. Moreover, Iran increased its defense budget by 32.5 percent this year, and its experience in Syria could influence how it spends the portion earmarked for arms purchases -- which may grow in the coming years as nuclear sanctions are lifted. Cooperation in Syria could also spur the sale of advanced Russian weaponry to Tehran.

OFFSHORE NUCLEAR ACTIVITIES?

With Iran's nuclear program potentially constrained by the P5+1 deal, some disgruntled IRGC officers might lobby the regime to continue nuclear R&D at offshore sites, beyond the prying eyes of international inspectors. While Iran and Syria are not known to have engaged in nuclear cooperation in the past, they might do so in the future -- as they have done in the missile field. Yet the urgency and fluidity of the battlefield situation make this an implausible scenario for the foreseeable future, as do concerns that such cooperation might come to the attention of Russia (which is a party to the nuclear accord) or Israel (which is better positioned to act against nuclear activities in nearby Syria than in faraway Iran).

DOMESTIC BACKLASH?

Thus far, Iran's involvement in Syria has not generated a public backlash at home, since the human costs have been borne largely by Tehran's proxies, while the financial costs are invisible to the average Iranian. If the conflict wears on and Iranian losses mount, the intervention may become a contentious political issue. Yet the proximity of the ISIS threat would likely keep any such dissent within bounds.

Michael Eisenstadt is the Kahn Fellow and director of the Military and Security Studies Program at The Washington Institute.