Why did states fail to balance against the United States after the end of the Cold War? Scholars have neglected an important dynamic: the accidental nature of America’s rise to primacy. The United States became the sole superpower not by deliberately increasing its capabilities but due to the unexpected collapse of its rival, the USSR. The case illustrates that a state’s responsibility for its gains in power can vary significantly, with important consequences for subsequent balancing. Active or deliberate power increases tend to produce more balancing than passive power increases because they signal aggressive intentions, alter the dyadic power balance between the rising state and potential balancers, and trigger loss aversion.