Russia controls this strategic slice of territory in the heart of NATO-allied eastern Europe

The Russian exclave of Kaliningrad is a political and geographic anomaly. Separated from Russia and situated on the Baltic Sea, the region is surrounded by NATO-member states Poland and Lithuania. It's closer to Berlin and Prague than it is to Moscow and St Petersburg.

On Tuesday, two Russian warplanes repeatedly carried out aggressive flight maneuvers against a US destroyer in the Baltic Sea. The Russian jets were operating out of Kaliningrad, which was 70 miles away from where the incident occurred.

Throughout the Cold War, Kaliningrad was as a dagger pointed at Scandinavia and Central Europe. That part of the Baltic coast was one of the most heavily militarized regions in the USSR. The exclave still has great military and strategic value for Moscow, especially given Russian president Vladimir Putin's appetite for stirring up trouble with his neighbors.

Russia's current military doctrine named Kaliningrad as one of three fronts for militarization and Moscow has previously sent nuclear capable missiles to the region as part of war game exercises.