On Sunday, the U.S. proposed an international coalition of the willing to aid Syria's opposition following a decision by Russia and China to block a U.N. effort to end the violent conflict. Secretary of State Hillary Clinton warned that a "brutal civil war" could unfurl and urged "friends of democratic Syria [to] support the Syrian people's right to have a better future." She added: "Faced with a neutered Security Council, we have to redouble our efforts outside of the United Nations." Since the coalition was floated, developments in Syria have only gotten worse, with the army shelling the city of Homs killing at least 50 people followed by the closure of the U.S. Embassy in Damascus. So what would an international intervention look like? Here are the scenarios U.S. officials, think-tankers, and military experts have envisioned. 

Libya Lite: U.S. officials speaking with the Associated Press said the intervention being proposed would share some similarities to the intervention in Libya. It would squeeze the Assad regime by "stepping up sanctions against it, bringing disparate Syrian opposition groups inside and outside the country together, providing humanitarian relief for embattled Syrian communities and working to prevent an escalation of violence by monitoring arms sales." Importantly, it would not involve coordination with NATO military operations to protect the civilian populations, a key pilar of the Libyan intervention. The AP reports that Syria's main opposition group, the Syrian National Council, is on board with the idea.

Air strikes Another intervention strategy is being floated by Shadi Hamid, a fellow at the Brookings Institution's Center for Middle East Policy. He emphasizes that he's not advocating an "Iraq-style invasion" with tens of thousands of troops but something lighter and surgical, such as "funding and arming the Free Syria Army, establishing 'safe zones' in the north and a targeted air mission to weaken the Syrian military's capabilities." Hamid argues that if the Syrian opposition formally requests military assistance, which they may in the near-future, "we have a moral responsibility to take it seriously." 

Wait for the opposition to mature, then strike Robert Pape, a professor of political science at the University of Chicago, says it's too soon to launch an intervention because there is no "viable, low-casualty military solution." That's because the Syrian opposition is different than Libya's opposition was in an important way. "Unlike Libya, where much of the coastal core of the population lived under rebel control, the opposition to Syria’s dictatorial president, Bashar al-Assad, has not achieved sustained control of any major population area," wrote Pape in The New York Times. "So air power alone would probably not be sufficient to blunt the Assad loyalists entrenched in cities, and a heavy ground campaign would probably face stiff and bloody resistance. If a large region broke away from the regime en masse, international humanitarian intervention could well become viable." 

Still, as many have pointed out, any Syrian intervention could be much more difficult than some have envisioned due to the strength and makeup of Syria's military. As Ben Rich of the Global Terrorism Research Center has pointed out, Assad's military is much more powerful than Qaddafi's was. "The Assad regime has spared no expense in outfitting itself with some of the most advanced air defence systems available on the international market, a practice spurred on by the 2007 Israeli strike on a Syrian nuclear reactor," he writes. "In Libya much of the air defence network was static and emplaced, Syrian air defence weapons are much more mobile, making their identification and suppression by attacking air forces problematic."