That Fifth Anniversary in Kosova

Over the next few days there will probably be even more references, in those media that cover Kosova in any depth, to the fifth anniversary of something or other that happened in a province that - tellingly - is one of the few territories in the world better known by the name that a minority of its population uses than by the name used for centuries by the historically substantial majority. But which event is it the fifth anniversary of?
We note that the final attempt at "ethnic cleansing" of the Kosovar Albanians was launched by the former Serbian regime five years ago today, in line with a concerted state policy ruthlessly pursued for 12 years before that - and thus long pre-dating either the creation of the Kosova Liberation Army (1996) or the criminally slow awakening of western interest in what was really happening in the former Yugoslavia.
Others, of course, prefer to emphasise the bombing of Serbian targets by NATO planes, and to assert that the bombing somehow "caused" the attempted genocide. But the bombing started four days later ...
From which one or other of just two conclusions can be drawn: either NATO has got much further with its research into time travel than anyone has yet realised, or many of the people who present themselves as experts on Kosova are fools, liars or worse.