Turmoil in the Balkans
We know that there are numerous economic and energy related projects as well as military projects in the Balkans, now that Russia successfully turned a corner in its own development, and has begun to really recover from the catastrophe of the collapse of the USSR. They have begun to become more robust in their foreign policy.
This has made the Balkans a new contest; this has made the Balkans a new area where now the US is concerned that NATO hegemony can be challenged. Now of course the east Balkans is more firmly in the grasp of NATO and the EU. In the West Balkans there was a war not very long ago involving former Yugoslavia, and they are more open to a multipolar form of policy.
This is very problematic for NATO. There are a number of projects, which the US is funding very actively. They still want to destabilize Serbia even though the government has been as open as possible to the needs of the US and EU. The government in Serbia understands the situation; they are surrounded by EU and NATO countries and the general gravity of the situation is that if they are to resist the EU in the short term, they must show their willingness to go in the EU's direction or a destabilization campaign may be launched.