The question of why states go to war has preoccupied political thinkers for centuries. While many explanations exist, two foundational perspectives offer starkly contrasting, yet equally influential, accounts: the state of nature articulated by Thomas Hobbes and the structural realism of Kenneth Waltz. Though separated by time and intellectual tradition, both thinkers locate the ultimate cause of conflict not in the specific grievances of individual actors, but in inherent, systemic conditions. Hobbes, in Leviathan, posits a pre-political "state of nature" where human beings, driven by self-preservation and a perpetual desire for power, exist in a condition of "war of all against all." This inherently anarchic existence, characterized by fear and suspicion, compels individuals to seek security, often through preemptive action, making conflict the natural and unavoidable state of human affairs. Waltz, writing in the 20th century, shifts the focus from individual human nature to the anarchic structure of the international system itself. In Theory of International Politics, he argues that the absence of a higher authority above sovereign states means that each state must ultimately rely on itself for survival. This self-help system, regardless of the internal characteristics of states or their leaders, generates conditions conducive to conflict, as states are incentivized to accumulate power to deter potential aggressors. Therefore, while Hobbes identifies the root of conflict in the individual's nature within an anarchic environment, Waltz locates it in the systemic pressures created by the absence of global governance.
Hobbes's conception of the state of nature is crucial to his argument for absolute sovereignty. He famously describes life without a sovereign power as "solitary, poor, nasty, brutish, and short." In this state, individuals are fundamentally equal in their capacity to harm each other. The pursuit of scarce resources, the desire for glory, and the pervasive fear of death lead to a constant state of competition and suspicion. War, for Hobbes, is not merely occasional fighting but a disposition towards it, a readiness to engage in violence when the opportunity arises. The only escape from this terrifying condition is the establishment of a sovereign authority, a Leviathan, capable of enforcing laws and maintaining order. This sovereign power, derived from the consent of the governed, creates a domestic peace by suppressing the natural tendencies toward conflict. However, it is important to note that Hobbes does not extend this notion of a sovereign to the international realm. Relations between states, in his view, largely resemble the state of nature, a condition of perpetual rivalry and potential conflict, albeit one where outright war is often tempered by prudence and the immense costs involved.
Waltz, conversely, grounds his theory in the structure of the international system. He identifies three "images" or levels of analysis that can explain war: the individual (leaders' characteristics), the internal characteristics of states (regimes), and the international system itself. While acknowledging the relevance of the first two, Waltz argues that the third image, the structure of the international system, offers the most powerful and parsimonious explanation for the recurrence of war. The international system, for Waltz, is defined by its anarchic nature – the absence of a central authority. This anarchy, he contends, forces states to behave in certain ways, regardless of their internal politics or the personalities of their leaders. States are the primary actors, and their overriding goal is survival. In an anarchic system, survival is best ensured through self-help, meaning states must provide for their own security. This leads to a "balance of power" dynamic, where states seek to prevent any single state from becoming too dominant. The pursuit of security, therefore, can paradoxically lead to insecurity, as states perceive the power accumulation of others as a threat, prompting them to increase their own capabilities, creating a dangerous spiral.
Comparing their approaches reveals both convergence and divergence. Both Hobbes and Waltz see anarchy as the fundamental condition that fosters conflict. For Hobbes, it is the anarchy of human nature in the absence of a social contract. For Waltz, it is the anarchy of the international system in the absence of a world government. However, their solutions, or lack thereof, differ. Hobbes's solution is the creation of an absolute sovereign to domesticate human nature. Waltz, while recognizing the dangers of international anarchy, does not propose a world government as a solution, seeing it as practically impossible and potentially undesirable due to the concentration of power it would entail. Instead, he focuses on understanding how states manage within this anarchic structure, emphasizing the role of power balancing and the security dilemma. The "war of all against all" in Hobbes's sense is the potential outcome of the systemic pressures Waltz describes, where the self-help system and the security dilemma can escalate into widespread conflict if not managed through a prudent balance of power. Ultimately, both thinkers offer a sobering view of international relations, suggesting that conflict is not an anomaly but an inherent feature of systems lacking overarching authority, whether that authority is internal to human nature or external to the state.