Recently, there has been a remarkable collapse in the ability of dictators to maintain power. The dictator model has hitherto been straightforward: control the army through kin in senior positions and deploy pre-emptive repression. In the softer dictatorships, this has broken down because protest can no longer be pre-empted. The calculus of protest depends upon the number of people who are expected to turn out; there is safety in numbers. The new technology enables co-ordination and so has made protest much safer, hence Tunisia and Egypt.

The Syrian regime is not of this type: it is willing to kill protesters en masse. About one in 10 are getting injured, a rate so exceptional for mass protest that it calibrates both the courage of citizens and the depravity of the regime.

Rebellions in Ivory Coast and Libya show that even such grotesque regimes are vulnerable. This new vulnerability depends upon a sequence in which a triggering event initiates crucial defections by members of the army.

Step one is popular opposition on a scale that forces the regime to choose between ceding power and an action that crosses a red line. In Ivory Coast, the red line was the refusal of Laurent Gbagbo, the then president, to accept the UN-certified result of an election. In Libya it was the ugly public threats of vengeance: “We’ll find you in your cupboards”. For months, Mr Assad was able to suppress protest without quite crossing such a threshold. That time has long gone.

Step two is the financial squeeze on the government by international action. The regimes most exposed are those such as Syria whose revenues are drawn from natural resource exports, rather than taxation of the domestic economy. It is not just sanctions: international companies dare not besmirch their reputations by association with the morally toxic. As revenues are squeezed, army officers realise their future pay is in jeopardy.

Step three is for the opposition to coalesce around common leadership. It encourages senior officers to defect by rewarding them with leadership positions: in Syria two generals and an oil minister have already swapped sides. Enhancing the opposition in this way is critical: the interest of the army becomes aligned with regime change. Once this sinks in, the end-game is clear.

Step four is for the international community to incubate the military capability of the opposition. In its early stages, opposition is vulnerable, but Libya and Ivory Coast demonstrate that the rebel army does not need to be anything like as strong on paper as the government army in order to win. Victory is far more rapid, and far less bloody, than predicted by military pundits.

Financial sanctions radically change the fundamentals of combat because they change the self-interest of the officer corps. Beyond the officers, the army rank and file largely lacks interest in participating in violence against its own people. In Libya, the opposition was even weaker than the Ivory Coast’s successful Forces Nouvelles, but once incubated by air cover from Nato and arms from friendly regimes, the officer corps made the same calculation. Military defeat for the regime came because, as the climax approached, the army evaporated.

The Syrian regime has survived for so long not because of its military strength but because it avoided crossing a red line of international outrage. Homs was that red line: the dead of Homs did not die in vain.

What remains is the diplomatic shuffle to enable the rebels to be protected and armed. This will doubtless be embarrassingly confused and dissimulating, couched in the language of humanitarian concern.

Kofi Annan has corralled the UN Security Council into resolutions with which the Assad regime is now visibly failing to comply: slaughter of protesters continues despite the “ceasefire”. Russia’s covert military support for Mr Assad will be put into the open, making a mockery of its public stance of opposing international military protection of the opposition. Asma al-Assad will continue to oblige: the regime will shop till it drops. Such developments will enlarge the space for some governments to muster the modicum of necessary gumption. But despite military timidity, the financial boa constrictor will keep on tightening.