(CNN) -- While the world's attention was focused on Boston and North Korea, the conflict in Syria entered a new phase -- one that threatens to embroil its neighbors in a chaotic way and pose complex challenges to the Obama administration.
What began as a protest movement long ago became an uprising that metastasized into a war, a vicious whirlpool dragging a whole region toward it.
Many analysts believe the United States can do little to influence -- let alone control -- the situation. And it could make things worse. Fawaz Gerges of the London School of Economics argues against the United States "plunging into the killing fields of Syria ... because it would complicate and exacerbate an already dangerous conflict."
Others contend that if the United States remains on the sidelines, regional actors will fight each other to "inherit" Syria, and hostile states such as Iran and North Korea will take note of American hesitancy. They say inaction has given free rein to more extreme forces.
And in the wake of the strikes against Damascus, apparently by Israeli planes, critics argue that Syrian President Bashar al-Assad is now more vulnerable than ever and U.S. intervention could help finish him off.
Republican Sen. John McCain has revived calls for a no-fly zone. And introducing legislation to arm the Syrian rebels in the U.S. Senate on Monday, Democratic Sen. Robert Menendez said: "There will be no greater strategic setback to Iran than to have the Assad regime collapse, and cause a disruption to the terror pipeline between Tehran and Hezbollah in Lebanon."
But more than two years since the revolt against al-Assad began, regional analysts say Syria is in danger of becoming the next Somalia, which collapsed into fiefdoms 20 years ago and has been stalked by anarchy, terrorism and hunger ever since. Except Syria would be worse. Its religious and ethnic fault lines extend across borders in every direction; Somalia's anarchy was largely self-contained. Somalia never had chemical weapons, nor the missiles and modern armor that make Syria one of the most crowded arsenals in the world.
And unlike Syria, Somalia was never central to a titanic struggle between different branches of Islam: Sunni and Shia.
Given that background, here are five reasons Syria's war suddenly looks more dangerous.
1: Israel and Hezbollah's proxy war
For two years, Israel has looked on with growing anxiety as brutal repression in Syria has become de facto civil war. Now a high-octane game of regional poker is under way. The Israelis have not admitted carrying out the devastating strikes of last week, but U.S. officials tell CNN they have no doubt Israel was responsible.
Why would Israel suddenly become an active participant? While much has been said about President Barack Obama's "red line" -- that the use of chemical weapons in Syria would make him reassess U.S. involvement -- the Israelis have a different threshold: the transfer of advanced missiles to al-Assad's ally, the Shiite Lebanese militia Hezbollah.
Their main worry, U.S. officials say, was the possible transfer of Iranian-made Fateh-110 missiles, whose accuracy would pose a new threat to Israel. A consignment of these ballistic missiles had recently arrived at Damascus' airport. Similarly, the second Israeli strike before dawn Sunday was on a "research facility" near Damascus where weapons destined for Hezbollah were kept.
According to Jane's Intelligence, Iran's Defense Ministry reported the test firing of an upgraded Fateh-110 last year, and the Iranian Aerospace Industries Organization claimed it had a range in excess of 180 miles (300 kilometers.)
Israel's motive was not to degrade the Syrian military. It was about sending al-Assad a message (copied to Iran and Hezbollah): "If you try to raise the regional stakes by passing a new generation of short-range ballistic missiles to Hezbollah, the response will be swift and severe."
Gerges, author of "Obama and the Middle East," told CNN that we are seeing "an open-ended war by proxy. ... On the one hand you have Israel, regional powers and the Western states; on the other hand you have Iran, Hezbollah and Syria."
Is Syrian war escalating to wider conflict?
Middle East analyst Juan Cole agrees, writing on his blog: "It is not that the Israelis and Hezbollah are in any direct conflict, but they are gradually both becoming more active in Syria on opposite sides. It is an open question how long this process can continue before the conflict does become direct."
One miscalculation could provoke a wider escalation.
The stakes for Hezbollah are enormous. For nearly 30 years, it has been sustained by Iranian and Syrian support. If Syria becomes a Sunni-dominated state, Hezbollah's "rear-base" vanishes, and suddenly it looks more vulnerable to its archenemy Israel, one of whose strategic goals is to counter the growing missile threat from the north.
Military analysts believe Hezbollah has an arsenal of some 50,000 missiles and rockets, supported by a sophisticated, hardened infrastructure that would be even harder to uproot than during its last conflict with Israel in 2006. Little wonder that Israel has deployed two of its Iron Dome missile-defense batteries in its northern cities.
Will the Syrians retaliate for the strikes, which they describe as a declaration of war by Israel? To do so would divert resources from the regime's battle for survival. Not to do so would convey an image of weakness in the face of the "Zionist enemy."
Al-Assad has a history of not retaliating against Israel, most notably when the Israelis took out what was purported to be a Syrian nuclear installation in 2007. According to Cliff Kupchan with the Eurasia Group, Israel has calculated that "Bashar al-Assad is incapable of fighting on two fronts, that Iran will keep its powder dry for a possible future conflict over its nuclear program, and that Hezbollah will not attempt significant retribution without approval from its sponsors."
But one risk to Israel is that in weakening the Assad regime, it may strengthen some of the best organized and most potent rebel factions: jihadist groups such as the al-Nusra Front, which has already declared its affiliation with al Qaeda in Iraq.
2: More than ever, it's sectarian
In the early days of the Syrian uprising, people who were anti- and pro-regime shared one common dread: that Syria would descend, Bosnia-style, into sectarian horror. Now, in the fight to prevail, that has become a reality.
Moderates have been sidelined, and despite efforts to revitalize the opposition's political leadership in exile there is still no umbilical cord between the government-in-waiting and the fighters inside Syria.
The Free Syrian Army coexists with a strong Sunni jihadi element, while the regime is mobilizing "irregular" Alawite militia and Hezbollah fighters.
Syria's (largely Sunni) rebels say hundreds if not thousands of (Shia) Hezbollah fighters are now fighting for the Assad regime. Hezbollah's secretary-general, Hassan Nasrallah, said last week that his party would not stand by and watch the Assad government fall. Regional analysts believe there is a very real risk that along the poorly marked Syrian-Lebanese border, Sunni jihadists will come up against Hezbollah units, setting off a vicious war-within-a-war.
The Syrian opposition sees Iran and Hezbollah everywhere. The head of the UK-based Syrian Observatory for Human Rights, Rami Abdel-Rahman told the newspaper Asharq al-Awsat that "Iranian and Hezbollah officers are running the operations room in the battle for Homs and are controlling the army operations in the city."
He warned of "massacres against the Sunni community living in the besieged areas if the army captures these areas."
Such massacres were reported in the past week in the coastal Sunni enclaves in Baniyas and al-Bayda. The State Department said over the weekend that "regime and shabiha forces reportedly destroyed the area with mortar fire, then stormed the town and executed entire families, including women and children."
3: Al-Assad goes for broke?
After being on the defensive for months, the Syrian regime has recently launched a series of brutal counterattacks against areas controlled by rebel factions, seeking to restore precious lines of communication and reconnect Damascus with other parts of the country. In so doing, it appears Assad has relied even more on the shabiha -- loyalists with an existential stake in the regime's survival.
As veteran Middle East watcher Anthony H. Cordesman of the Center for Strategic and International Studies has put it: "The Assad regime seems ready to escalate in any way it can to either preserve power or effectively divide the country."
Among the areas where this counteroffensive has been most intense is Daraya, south of the capital, which has been reduced to ruins on the principle that "if we can't control it nor shall you." To the east of Damascus, regime forces have encircled rebels in the Gouta region, relieving the immediate threat to Damascus airport, which is at one end of the critical air bridge between Syria and Iran.
As critical as these areas around Damascus is the town of Qusayr between Homs and the Lebanese border, once home to 50,000 people. Videos uploaded in recent days show the regime pouring artillery fire into the town and conducting airstrikes from above; whole blocks have been demolished. Claims emerged Wednesday from opposition sources of new massacres around the town.
Qusayr sits astride one route to the Syrian coast and another to the Lebanese border. For the rebels, holding Qusayr is important because it's another way of strangling the regime's ability to sustain itself, and it complicates Hezbollah's access to Syria.
The signs are that al-Assad is investing heavily in trying to break the rebels' hold in key parts of south and central Syria, reversing the gains they had made in a series of hard-won victories last year.
Short of forceful foreign intervention, some military analysts argue for tying al-Assad's hands behind his back by providing the rebels with more anti-armor and anti-aircraft missiles and a communications infrastructure. More ambitiously, some say the international community should enforce what might be called a "no-move" zone, selectively picking off regime forces from the air or with missiles.
In essence, that's what NATO's mission in Libya became. But it would take considerable airpower and the use of facilities across the region to gain control of the Syrian sky. The chairman of the U.S. Joint Chiefs of Staff, Gen. Martin Dempsey, said at the end of April: "The U.S. military has the capability to defeat that system (of Syrian air defenses), but it would be a greater challenge, and would take longer and require more resources" than in Libya.
4: Chemical Weapons
For much of last year, Obama's "red line" seemed a largely hypothetical one. But as al-Assad's situation grows more desperate and control of chemical weapons stocks more difficult to guarantee, there are indications that some chemical agents have been used in limited quantities in places like Daraya. The questions are: how much, of what and by whom?
The announcement by a senior U.N. official Monday that rebels may have used sarin gas during an operation near Aleppo in March means this red line is even more difficult to discern. The U.N. commission subsequently said it "has not reached conclusive findings as to the use of chemical weapons in Syria by any parties to the conflict."
Establishing "custody" and the systematic use of such weapons is very difficult in the absence of monitors on the ground.
A U.S. State Department official on Monday would say only: "We take any reports of use of chemical weapons very seriously and we are trying to get as many facts as possible to understand what is happening."
But understanding and countering the threat are miles apart. The Pentagon estimated last year it might take 70,000 troops to secure or destroy Syria's massive stockpiles -- and the situation on the ground has deteriorated since then.
In Cordesman's view, "Any U.S. forces that tried to deal with the chemical weapons in Syria through ground raids would present the problem of getting them in, having them fight their way to an objective, taking the time to destroy chemical stocks, and then safely leaving."
5: Players and Puppets: Iraq, Turkey, Lebanon and Jordan
Syria is surrounded by neighbors with a stake in influencing the outcome of its civil war. Most -- and other more distant states such as Qatar and Saudi Arabia -- are backing their own factions as well as supporting the "government-in-waiting." Now more than ever they feel the force of that whirlpool.
Iraq's beleaguered Sunni minority is more and more in confrontation with a Shia-dominated government in Baghdad allied to Iran. The Sunni tribes of Anbar and Ramadi have historical connections with their brethren across the border and would welcome a Sunni-dominated government in Syria as a valuable counterbalance to a hostile government at home.
For more than a year, there have been persistent reports of weapons crossing the border to help the Syrian resistance and evidence of co-operation between Syrian and Iraqi jihadists. Resupply convoys headed through Iraq to the Syrian regime have been ambushed in recent months.
In the view of Ian Bremmer, president of the Eurasia Group, "Iraq is teetering back towards civil war, with direct implications for the investment climate across the country, and deepening geopolitical conflict between Iran and the Sunni monarchies" of the Gulf.
Turkey is also growing alarmed at the prospect of a more "Balkanized" Syria. It already has 322,000 refugees on its soil, according to latest figures from the UNHCR, the U.N. refugee agency, with another 100,000 clamoring to cross.
Turkish Prime Minister Recep Tayyip Erdogan has upped his rhetoric in recent days, criticizing the Israeli strikes but reserving his most passionate denunciation for the Assad regime.
"You, Bashar Assad, will pay for this. You will pay heavily, very heavily for showing courage you can't show to others, to babies with pacifiers in their mouths," he told an audience over the weekend.
But Erdogan is struggling to turn indignation into influence. As the International Crisis Group noted in March: Turkey "now has an uncontrollable, fractured, radicalized no-man's-land on its doorstep."
The Jordanians know how that feels. They are trying to cope with 450,000 Syrian refugees -- equivalent to some 7% of the Jordanian population -- growing restless and desperate in makeshift camps. The number in Lebanon has shot up to 455,000, according to the United Nations. In all, the Syrian conflict has generated an extra half million refugees in just two months.
Lebanon -- whose sectarian equation mirrors that in Syria -- cannot help but be dragged into the war next door. Several Salafist sheikhs in Lebanon have declared jihad against the Syrian regime in response to Hezbollah's growing involvement. One of them, Sheikh Ahmed Assir, called on Sunnis in the city of Sidon to form brigades to help the resistance in Qusayr. And rocket fire, apparently from the Free Syrian Army, has landed in Shiite areas around the Lebanese town of Hermel.
A land of bad options
Some critics of the Obama administration say there is a moral imperative to intervene in Syria in the face of slaughter (at least 70,000 Syrians have died so far.) In the Washington Post, former Obama adviser Anne Marie Slaughter has recalled the "shameful" failure to confront genocide in Rwanda.
But Cordesman writes: "Syria has become the land of bad options. The Obama administration has reason to hesitate in intervening."
And Joshua Landis, who runs the blog Syria Comment and is director of the Center for Middle East Studies at the University of Oklahoma, warns that even "a humanitarian intervention will become a nation-building project, as was the case in Iraq."
With the number of internally displaced now put at 4.25 million people, that would be a huge project.
The dream among diplomats a year ago was that a moderate opposition could be brought together with some regime elements to ease al-Assad from power. As the Syrian war threatens to become a regional one, the United States and Russia are dusting off that option, calling for an international conference within weeks that would be attended by both the government and the opposition.
"The alternative is that Syria heads closer to the abyss, if not over the abyss and into chaos," said U.S. Secretary of State John Kerry.