Six months after the Syrian uprising began it seems clear that peaceful protests aimed at overthrowing the regime and ousting President Bashar al-Assad have failed. With no prospect of meaningful national dialogue in sight, the conflict now appears to be shifting into a new, infinitely more hazardous phase: the weaponisation of the revolution. Syria is moving inexorably from Arab spring to an ever darker, dangerous winter of discontent.

The inability of unarmed civilian demonstrators to bring down Assad, or at least bring him to the negotiating table, has several causes. One is the lack of a unified, well-led opposition with clear objectives. The exiled "Syrian national council", whose formation was announced in Istanbul last week at the second attempt, would like to emulate the success of Libya's rebel National Transitional Council. But the grouping faces a credibility gap at home and abroad.

"This time it is imperative that they find common ground. A single voice will help convince Russia, China, India and Brazil – all of which continue to support the Assad regime – to take a stand against the bloodshed," said an editorial in the UAE newspaper the National. "A unified alternative to the regime will begin to convince the international community at large that it is safe to invest in the opposition."

A second key factor is the unexpectedly brutal tactics used by Assad and his security forces. At least 2,700 civilians have been killed and many more injured, according to the UN. Credible reports of torture, rape and summary execution abound. The pressure is relentless; yesterday squadrons of tanks were bombarding the city of Homs. Assad was habitually portrayed as a softer version of his late father, Hafez. But the past months have shown a vicious side to his character that few suspected.

Ambivalence bordering on pusillanimity among Arab and western leaders has also undercut the revolution.

From the outset the US, Britain and France made clear there would be no Iraq-style military intervention. They clung tenaciously to the received narrative: that Assad was at heart a reformer who could be induced to change. Belatedly, Washington and London have decided he has lost all legitimacy and must go. But beyond speeches and sanctions, they are doing little to achieve that goal.

Syria's neighbours have been equally ineffective. Recep Tayyip Erdogan, Turkey's prime minister, reiterated his view at the weekend that Assad was finished. "You can never remain in power through cruelty. You can never stand before the will of the people," he told CNN.

Historically speaking, that's a highly dubious assertion. In any case, Turkish policy appears petrified by the turmoil on its southern flank. Saudi Arabia and Israel, though no friends of Assad, value stability above all else, while Iran and Hezbollah in Lebanon have maintained their support for Damascus despite misgivings.

The belief that revolution could prevail through peaceful moral suasion and popular pressure was always misplaced, argued Gary Gambill in Foreign Policy. "There are no plausible circumstances under which a democratic transition would constitute a rational choice for the embattled dictator," he said.

"The crux of the problem is Syria's unique minority-dominated power structure … Alawite solidarity renders the loyalty of the internal military-security apparatus nearly inviolable, enabling Assad to mete out a level of repression far beyond the capacity of most autocrats." To surrender power would be suicidal for Assad, he argued.

Recognising peaceful protest is failing but that the uprising has gone too far to simply peter out, US officials are reportedly anticipating the escalation of organised violence in Syria. "In co-ordination with Turkey, the United States has been exploring how to deal with the possibility of a civil war … a conflict that could quickly ignite other tensions in an already volatile region," Helene Cooper of the New York Times reported from Washington.

A former Obama administration official added: "The Sunni [majority] are increasingly arming, and the situation is polarising."

This disturbing assessment matches those in the region where attention is focusing on a group of defectors, the "Free Syrian Army", which is organising armed resistance.

"It is the beginning of armed rebellion," General Riad Asaad, the group's leader, told Liz Sly of the Washington Post. "You cannot remove this regime except by force and bloodshed."

Like the Libyan rebels in Benghazi, the group's stated aim is to secure a safe haven in northern Syria, win international backing for a no-fly zone, and launch a military campaign to topple Assad.

Al-Jazeera's special correspondent Nir Rosen, who recently travelled through Syria, said the writing was on the wall. "As I spent more time in Syria, I could see a clear theme developing in the discourse of the opposition: a call for an organised armed response to the government crackdown."

A senior opposition figure in Damascus told Rosen: "In the end we cannot be free without weapons."

It seems the war for Syria's future is about to begin in earnest.