The Kurds are only a minority in North Syria. What we are seeing is an excuse for a land grab which was green lighted for the benefit of bottom feeder voters in both the US and Turkey. Christians are kissing their Bibles prior to joining the fray (and the likelihood of death and defeat) against Islamo -fascist militias.
The North Syrians may be betrayed by Russia as well as the US. If Assad behaves as stupidly as he has done repeatedly over years past all will be lost. Essentially it's up to Assad. He will either incorporate another 20-30,000 highly trained troops into an otherwise depleted army or Syria loses its north to an al Qaeda styled mini-state for good.
