Syria is a proxy war.
Experts on the Levant often brandish this term in an attempt to justify why the ongoing civil conflict in Syria continues to roil in bloodshed, causing more than 110,000 deaths in its two and a half years.
Foreign intervention is one of the chief causes behind its longevity, they say. American support for logistics, humanitarian aid and, recently, weapons has certainly bolstered the ability of rebel opponents to take on the military strength of the Bashar Assad regime.
But many with intimate knowledge of the region nod toward the more subversive intentions of other regional powers. Iran and Saudi Arabia have a series of supply routes into that country, as well as other methods of support.
Here's what you need to know about those two country's involvement in the ongoing war in Syria:
Iran is predominantly Shiite Muslim. Saudi Arabia is predominantly Sunni.
"Their differences go back almost as far as the founding of Islam," says Theodore Kattouf, a career diplomat who served as U.S. ambassador to Syria in the early 2000s. "Saudi leaders have a conservative Sunni identity, and Iranian leaders have a Shiite identity."
Sunni Islam was the first major sect of the religion and represents the belief system for a vast majority of Muslims worldwide. The original division with the Shiite Muslims originates with a debate over who directly succeeded Mohammad, the prophet of God, as the second Imam or spiritual leader of the faithful.
"Both sides are capable of cynically employing these identities to motivate their partisans to fight one another," says Kattouf.
Divisions between the two sects have magnified culturally since Islam began in the 7th Century.
Roughly three-quarters of Syria is comprised of Sunni Muslims. It has been ruled, however, since 1971 by the Assad family who are ethnic Alawites, a Shiite sect that has been historically persecuted by the Sunnis.
"Saudi Arabia sees Syria as an overwhelming Sunni Muslim country in which Shiite Iran has propped up a minority-dominated regime," says Frederic Hof, an ambassador and political appointee who served as special adviser to President Barack Obama for the transition in Syria.
"When the regime reacted violently to the initial waves of peaceful protests in 2011, Saudi Arabia processed those events as Iran-abetted sectarian slaughter directed at Arab Sunnis," he says.
Saudi Arabia sees Syria as a vital member of the Arab community, says Hof, now a senior fellow at the Atlantic Council, and believes Iran's intervention in Syria is a "totally inadmissible symptom of Iran's attempt to penetrate the Arab world."
Saudi Arabia is also home to Mecca and Medina, two of the most sacred places for Muslims. Iran hopes to rob it of some of that influence, says Kattouf, now president of Amideast.org.
"[Iran] has become the defacto Shiite power in the region," he says. It hopes to be "in the vanguard of all Islamic groups" in the region, by challenging Saudi Arabia for its holy places, and trying to appeal to Sunnis as well as Shiites.
Syria at one point was considered the center of the known world, not in the least for its geographic position at the crossroads of ancient cultures.
(And, speaking of religion, Damascus was one of the first places to receive the Christian ministry of St. Peter).
It remains a key strategic point, particularly for Iran.
Reza Kahlili is the nom-de-plume for a native Iranian, who claims to have served in the elite Iranian Revolutionary Guard Corps before defecting to spy for U.S. intelligence services.
"[Syria] is the corridor that connects Lebanon and Iraq, and the combination of activities in both regions, with the hopes of creating instability in Jordan and crushing Israel," he tells U.S. News.
Kahlili says the Guard has been operating in Syria through small bases since the early daysof Iran's revolutionary government. It has established command and control centers and monitors Islamic extremist movements from there. It also trains and supplies organizations such as Hezbollah, the Lebanese militant political party that has sent an undisclosed number of fighters in support of the Syrian regime.
The fearsome IRGC was formed in the wake of the 1979 revolution by Ayatollah Khomeini, and reports directly to the supreme leader. Some of Kahlili's claims, compiled in his book "A Time to Betray" have been met with skepticism, though the Washington Post's David Ignatius confirmed at least his relationship with the CIA.
"To this day, they have bases in Syria," he says. "The fall of Assad could ruin their plans. Saudi Arabia knows this."
Iran needs Syrian access to neighboring Lebanon to continue to shape politics there, says Kahlili and other experts on the region, as well as to intimidate neighboring Israel.
The Atlantic Council's Hof refers to Syria as Iran's "logistics bridge."
"Hezbollah's missiles and rockets pointed at Israel are Iran's first line of defense: a strong deterrent as Israel thinks about attacking Iranian nuclear facilities," he says.
"Assad has been willing to subordinate Syria's national security interests to those of Iran with respect to Hezbollah," adds Hof. "Iran fears - probably justifiably - that any successor Syrian government would either bring the Hezbollah relationship back to what it was before Bashar Al Assad assumed power or eliminate the relationship altogether."
Whether as an attempt to become a hegemonic power, or simply establish security in neighboring countries, both Iran and Saudi Arabia are intent on carrying a big stick, as well as speaking loudly.
Iran's intervention in Syria may be a symbol to the world that it is a force worth fearing. It is also believed to be actively involved in citing insurrection in Bahrain, an island in the Persian Gulf immediately off Saudi Arabia's coast.
"The Saudis have a bigger tent," says former ambassador Kattouf of that country's foreign influence. Saudi Arabia has long been an ally of the U.S. and receives significant military support, including arms sales. The Iranians tried to have a bigger tent, he says. But their support for Assad has left many regional countries skeptical of their true intentions, and has isolated Iran throughout much of the Middle East.
"[Iran] has an expansive agenda," says Kahlili. "They have infiltrated Africa, set up many collaborations with African nations, and through collaboration, they export arms, narcotics and other things."
Both Iran and Saudi Arabia are trying to influence the Sunni hardliner Muslim Brotherhood in Egypt, these experts say. Kattouf adds this becomes increasingly difficult for the Saudis, who have historically been very discriminating in which Sunnis they are willing to endorse. For example, the Saudi monarchy denied native son Osama bin Laden's request in the 1990s to employ the group of fighters he had raised to combat the Russians in Afghanistan and turn their attention to striking America.
"Saudi Arabia, even for someone who follows the region, is quite honestly hard to explain in their policies," says Kattouf. "Not all Sunnis in the opposition get their blessing or their support.
"They do pick and choose who among the conservative Islamic factions in Syria, of which there are many, they will support."
Relations with the West
Saudi Arabia has grown increasingly concerned about recent Iranian overtures to the U.S., and subsequent attention from the Obama administration. Kind words leading up to the U.N. General Assembly in late September could be the first break in more than three decades of tense diplomatic relations between the two nations. Iran hopes this will lead to an easing on sanctions against its worrisome nuclear program.
"It's deeply unsettling to the Saudis," says Kattouf. "And they may be exaggerating prospects for success."
Iran's latest goodwill tour may be seen as its attempt to break in on the historic alliance with Saudi Arabia, one of the world's most significant recipients of American military resources.
The Saudis should welcome an agreement that prevents Iran from acquiring weapons banned by the U.N., he says, and they've never wanted to see the U.S. go to war with Iran.
"They almost wanted a magic solution, and this is as close as they're going to get," the former ambassador says.
"Iran has analyzed that [in] holding direct talks with the Obama administration, the minimum would be that further sanctions would be avoided," says Kahlili. "Now the White House has the hope that something could come about."
"At the end of the day, it's not going to stop the nuclear program," he says.
Former ambassador Hof says these talks could lead to some good in Syria.
"If there is a nuclear deal between Iran and the West, one that removes the possibility of an Israeli military campaign against Iran, it is possible that the struggle for Syria involving external players may wind down," he says. "But Iran will always support Hezbollah in Lebanon in any event, even if it becomes a peaceful political movement."