Twice in the past month, African armies have announced that they will defend the right of civilian activists to take to the streets with their calls for democracy and for an end to corruption and nepotism. And twice it seems the soldiers - in Tunisia and in Egypt - are positioning themselves as catalysts in the downfall of tyrannies. It would be wrong to put much faith in the military's powers of social transformation: a succession of self-proclaimed corrective juntas have failed woefully to make the promised political or economic reforms. The combination of military-backed reform, new constitutions and political parties, new electoral commissions and then monitored elections can produce stability and coherence if the political activists stand firm enough. If they fail, a new generation of political soldiers takes over and entrenches a type of militarised rule with decorative elections. That danger now confronts Tunisia's and Egypt's democracy movements. Will the brave oppositionists who have confronted the old militarised dictatorship be able to work with the soldiers to establish a new political order or in the end will the military find the prospect of real change unpalatable? Both Tunisia and Egypt are on the brink of change in which the military can play a positive constitutional role, but both societies still run the risk of a rapid reversion to autocracy if that fragile trust between activist and soldier breaks down.