Whenever it appeared negotiations and UN Shuttle dimplomacy started to stablize the situations in Kosovo, they would attack in the most brutal ways and invited retaliations by Serbian Security force. They did it intentionally and without mercy and they finally provided the pretext needed by the EU and the US to act. 

THere is enough pretext for the US to act now. The war is on and only question is whether it is a slap on the wrist or or it has more lasting effect on Syria.