A vote in Kosovo's parliament this week that approves formation of its own army for the first time puts the 4000 NATO troops stationed there in a difficult position. Kosovo doesn't have a proper military. This is the Kosovo Security Force, a lightly armed unit, mostly used for civil defence, natural disasters, and the like.
They're not part of NATO, but they do receive training from the alliance, seen here. The problem is that the wounds of the Balkan wars in the 1990s, from which Kosovo first emerged, are still fresh. NATO protects Kosovo, but it's also been a peacekeeping force there ever since those wars.
NATO's position is that if Kosovo wants an army, they should only do it with the approval of the Serb minority that lives in Kosovo. And simply put, Serb law makers don't approve. 11 Serb members of parliament boycotted Thursday's vote and have blocked past efforts for years. NATO says this development may force the alliance to reconsider its mission here, although it's unlikely to abandon it completely.
Kosovo's governed by a nationalist party, but most other parties do support militarization with the hope of joining NATO someday. Its Prime Minister visited the troops over summer.