Tensions escalated this week with cross-border clashes between Turkish forces and the YPG near the Syrian border.
Islamic State controls parts of Iraq and Syria and has broadcast its beheadings of journalists and aid workers over the past few years.
The solution to the mess has to be based on a division of Syria and Iraq into four new countries, on an ethnic and religious basis, to provide each one of the various groups with a sense of security.
Massacres committed by Islamic State against Yazidis mean they “can’t trust their Sunni neighbors again.”
The incident is widely considered to have been an attempt to elude the fate of a Jordanian pilot whose burning execution was popularized by the Islamic State propaganda machine.
Next month, Bashar Assad will mark 15 years to coming to power and while he is still hanging on in parts of the country, his father’s estate has been irreversibly split.
Cantlie has appeared in a series of documentary-style propaganda videos since he was captured in late 2012.
YouTube shows the Caliphate's clumsier side
The United States is leading an international coalition against the extremist terror group and an air campaign against IS fighters in Iraq and Syria began in August.
Syrian Observatory for Human Rights said incident showed such execution-style killings were not confined to the militant Islamic State group.