For Iraq's Shiite-led government, the Syrian civil war has made the job of balancing the demands of Baghdad's main patrons, the U.S. and Iran, even more difficult.
Last month, Iraqi Prime Minister Nouri al-Maliki came under pressure from Washington to ban Iranian planes suspected of carrying weapons to Syria from using Iraqi airspace. Sticking to official neutrality on Syria, al-Maliki said he'd try, but that Iraq could at best perform spot checks.
The fighting spirit of Syria's Sunnis, meanwhile, has helped embolden a Sunni insurgency in Iraq that had been withering for years. If Assad is defeated and Syria joins a Sunni coalition in the region, Iraq might find itself seeking even closer ties with Iran.
Turkey's outspoken support for the Syrian rebels — a policy it adopted in August 2011, after trying to reason with Assad first — has coincided with a sharp rise in increasingly brazen attacks by the separatist Kurdistan Worker's Party, or PKK, in southeastern Turkey.
In August, Turkey's deputy prime minister, Bulent Arinc, said a number of those attacks were apparently carried out by Kurdish gunmen who infiltrated from Iran, a staunch Assad ally. A Turkish pro-government newspaper, Sabah, has claimed that Iranian intelligence has stopped providing Turkey with information about Kurdish rebel infiltrations.
Assad has also used Syria's Kurds as pawns against Turkey.
After Turkey repeatedly raised the idea of internationally enforced safe zones in Syria in the spring, Syrian regime forces withdrew from several Kurdish towns on the border with Turkey over the summer. That granted them unprecedented autonomy, but also set them up as a buffer zone.
Assad was telling Turkey: "'You can intervene (in Syria), but you're going to have to fight the PKK on the way to get there'," said Soner Cagaptay, a Turkey expert at the Washington Institute for Near East Studies.
Picking a side in Syria also seems to have ended a decade-long effort by majority Sunni Turkey to increase its regional influence by getting along with all players, including Iran.
In Jordan, the biggest problem for now seems to be the strain put on the country's meager resources by some 200,000 Syrian refugees who have flooded across the border.
Israel has tried to stay on the sidelines, but last month sent a clear message that it's prepared for all scenarios. In a snap military drill, it airlifted thousands of soldiers to the Golan Heights, a strategic plateau Israel captured from Syria in 1967, and carried out live fire drills there.
Israel could face a serious threat to its security if Syrian territory near the Golan becomes a chaotic no-man's land, said Giora Eiland, a former national security adviser in Israel. Last week, Syrian mortar shells fell near a Golan apple orchard, but Israel said it did not believe it was an intentional hit.
However, Iranian advisers are helping direct the Syrian regime's battles, the defected Syrian prime minister said last month. This would put them just a frontier away from Israel at a time of increasingly ominous threats between Israel and Iran over Tehran's suspected nuclear weapons program.
Nerguizian, the Washington analyst, said Syrian conflict has set in motion sweeping changes that will transform the region.
"At this rate, it is not going to look anything like the pattern we've seen in the past few decades, since the end of World War II," he said.
Associated Press writers Suzan Fraser in Ankara, Turkey, Barbara Surk in Beirut and Lauren E. Bohn in Jerusalem contributed reporting.
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