The Suwalki gap is about 60 miles long, a stretch of land found on Poland's border with Lithuania. Its vulnerability could decide the fate of the Baltic states.
The land connects the Russian enclave of Kaliningrad with Belarus, known for being a Moscow ally. Its possible exposure to Kremlin control is a source of worry for U.S. officials, the Wall Street Journal reports.
If Moscow gained control of the corridor the Baltic States would, catastrophically, be cut off from other NATO allies. The U.S. will lead a deterrent force from April 2017 based at the Suwalki gap in an attempt to secure the area.