This document provides an introduction and overview of a case study on the rapprochement between Belarus and Russia in response to NATO expansion. It notes that NATO expansion led Belarus and Russia to strengthen their military cooperation and alliances in order to counter perceived security threats. Some key developments included the two countries establishing a joint air defense system and conducting large military exercises portrayed as responses to potential NATO aggression. The document also analyzes how Belarus' strategic location bordering both Russia and expanding NATO states makes it an important geopolitical player in the region.