“Kosovo je Srbija” (Kosovo is Serbia) is the most famous slogan in Serbia, and its use has gathered steam in the past five years to protest Kosovo's declaration of independence.
Despite this fact, a Turkish prime minister arrives in Kosovo and pokes his finger in the eye of Serbian nationalism by saying “Kosovo is Turkey” before a cheering crowd. One would expect Turkish diplomats to warn the prime minister against uttering such insensitive phrases. "You know, Mr. Prime Minister, our foreign minister worked long and hard to restore peace with the Balkan nations. At the end of the day, there is no reason to wake up a sleeping monster: Serbian nationalism," they could have said.
A few centuries back, it was easier to do diplomacy by making pragmatist calculations based on other states' relative power. Today, thanks to nationalism and democracy, diplomacy has become much harder, because leaders are accountable to their publics.