Exactly, what to look for in Greece's case? At which stage do you cancel your holiday? Burnings of northern European politicians in effigy, or something more serious? It's difficult to imagine an EU member state to which I can (almost) hop on a plane without a passport going to pieces like that. Greece seems very much 'one of us', unlike the 'other' that is everywhere East of the Med. Not least their NATO membership. But I'm aware that we blindfold ourselves to stuff we don't want to see until it's too late, and then we all find it terribly inconvenient when we can't get feta and wonder 'how could this have happened?'.
Speaking as a spectator of history: In eighth grade, we went from "Ollie North on trial" to "Fall of the Berlin Wall." In ninth and tenth grade Europe and Asia gained a couple dozen new countries. In eleventh grade Soviet troops shelled the Kremlin and then, four months later, dissolved the USSR. Shit moves quick. In 1998 the only magazine writing about the Taliban was Glamour. Three years later we're bombing them.