The empirical limitations of classical realism’s focus on balances of power are well understood. The theory goes that states balance against other threats simply based on the arithmetic of military hardware, which leads to all sorts of nasty arms races and security dilemmas. Of course, empirically we see examples of states – particularly smaller states – not balancing against states with massive military power. The United States’ situation following the second World War, during the Cold War, and during its famous “unipolar moment” in the 1990s demonstrates as much. NATO and major non-NATO allies of the US could have easily perceived the American war machine coming out of World War II as a threat worth balancing against but instead they chose to side with the United States.
The explanation for this is simple and has been known since the late 1980s. States tend to balance against threats, not mere power. Stephen M. Walt first explained the phenomenon in an International Security article in 1985 and since then threat-based analysis has become somewhat of a mainstay among contemporary realists and Western foreign policy elites. Understanding how perceived threats shape foreign policy is invaluable for foreign policy makers. The entirety of Cold War strategic missile defense and proxy-state acquisition was based around the notion of maintaining a favorable game-state on the global chessboard based on the mutual threat perceptions between the United States and the Soviet Union. Ideology mattered to an extent in framing the distrust, but what really mattered in the creation of foreign policy was the notion of a monolithic external threat.