Why did realists criticize efforts to spread a single political ideology across the world?

Realists criticize efforts to spread a single political ideology—such as global democracy or communism—because they believe such "messianic" crusades obscure core national interests and threaten the survival of both individual states and the international system.1

According to realist theory, the international system is characterized by anarchy, meaning there is no central authority to enforce order. In this environment, states must prioritize their own security and survival above all else. Realists argue that:231

• Human Nature: Attempts to reform other countries toward ideals of universal trust and cooperation run counter to human nature, which is inherently inclined toward competition, conflict, and war.1
• Distraction from Interests: Ideological crusades can lead states to engage in misguided foreign adventures, distracting them from the intelligent pursuit of their actual national interests and the careful calculation of power.14
• Systemic Instability: By prioritizing ideological goals, states risk clashing with other powers, which can destabilize the balance of power and increase the likelihood of hegemonic conflict.13

Ultimately, realists maintain that foreign policy should be guided by pragmatic diplomacy and the recognition of the limits of power, rather than the pursuit of moral or ideological agendas.15