What fundamental assumption differentiates offensive realism from defensive realism?

The fundamental assumption that differentiates offensive realism from defensive realism lies in their views about the optimal amount of power a state should possess. Offensive realism, primarily associated with John Mearsheimer, argues that the anarchic structure of the international system creates strong incentives for states to maximize their relative power. Because the system is anarchic, meaning there's no central authority to ensure states' security, states constantly fear each other. Offensive realists believe that the best way for a state to guarantee its survival is to become the most powerful state in the system, ideally a hegemon. A hegemon is a state that is so powerful that no other state can seriously threaten it. Offensive realists argue that states are inherently aggressive and constantly seek opportunities to gain power at the expense of other states. They believe that states pursue a strategy of hegemony not necessarily because they are inherently evil, but because it is the most effective way to ensure their own survival. States should, therefore, always strive to increase their power and influence, even if it means taking risks and potentially provoking other states. Defensive realism, associated with Kenneth Waltz, posits that states primarily seek to maintain their position in the international system rather than maximizing their power. Defensive realists agree that the international system is anarchic and that states are concerned with survival. However, they argue that states should primarily focus on maintaining the balance of power and avoiding actions that could provoke a strong response from other states. They believe that aggressively pursuing power can be counterproductive because it can trigger a balancing coalition of other states against the aspiring hegemon. Therefore, defensive realists advocate for a more cautious foreign policy that emphasizes deterrence and maintaining the status quo. States should seek an appropriate level of power to ensure their security, but they should avoid seeking hegemony because it is ultimately self-defeating. The core difference, therefore, is whether states should actively seek to maximize power (offensive realism) or primarily aim to maintain their existing position and security (defensive realism).