On Sept. 14, Russia will hold one of its biggest military exercises since the Cold War. Tens of thousands of military personnel are expected to participate in the Zapad 17 drill, set to take place over seven days in Belarus, Kaliningrad, and Russia.

In the Suwalki Gap, the 64-mile border between Poland and Lithuania, tensions are high. This is the only border the Baltic states share with the rest of NATO. After Russia’s annexation of Crimea in 2014, some fear that the three countries (Lithuania, Latvia, and Estonia) could be next. Taking the Suwalki Gap would cut them off from their European NATO allies.

The United States is sending an increasing number of soldiers to supplement their NATO allies in Central and Eastern Europe in response to potential Russian military expansion.