Libya. :/
Gadaffi and his government kept a lid on that country for a long time. It was one of the most successful nations in Africa with the highest literacy rates in North Africa, the highest number of doctors per capita in North Africa. They made repeated overtures to the West to come in from the diplomatic cold. Then we allied with Qatar and destroyed the government, the infrastructure and the economy and turned it into a factory producing violent radicals and ISIS soldiers. Last I heard, they had three "governments" and two competing parliaments.
So the parents and two of their children went back there after Ghadaffi was deposed and then returned and then one of those children returns to carry out this attack. Completely unsurprising. And tragic.