Like most international relations scholars of his generation, Mearsheimer was deeply influenced by Kenneth Waltz, the founder of the school of international relations known as neorealism. Whereas classical realists such as Hans Morgenthau had traced international conflicts to the natural propensity of political leaders to seek to increase their power, neorealists (or structural realists) such as Waltz located the cause of war in the structure of international relations. In Waltz’s model the absence of an authority above states (the condition of anarchy) forces them to make alliances in order to contain the threats posed by rival powers. The international order, in other words, is determined by the balance of power between states. According to Waltz, the need for security leads states to favour the status quo and to adopt a defensive position toward their competitors.
Mearsheimer’s contrasting view, which he called “offensive realism,” holds that the need for security, and ultimately for survival, makes states aggressive power maximizers. States do not cooperate, except during temporary alliances, but constantly seek to diminish their competitors’ power and to enhance their own.
Mearsheimer based his theory on five core assumptions: (1) the international system is anarchic (there is no authority that exists above the states to arbitrate their conflicts), (2) all states have some military capability (however limited), (3) states can never fully ascertain the intentions of other states, (4) states value survival above all else, and (5) states are rational actors that seek to promote their own interests. Those conditions, according to Mearsheimer, “create strong incentives for states to behave aggressively toward each other.” Because states cannot know with certainty the present or future intentions of other states, he concluded, it is rational for them to attempt to preempt possible acts of aggression by increasing their military might and adopting an assertive position whenever their core security interests are at stake.
Although Mearsheimer recognized war as a legitimate instrument of statecraft, he did not believe that it was always justified. In fact, he was highly critical of the Iraq War (2003–11) and what he saw as an attempt by the United States to police the world. With regard to U.S. foreign policy, he advocated a strategy of “global balancing” rather than “global hegemony.” A superpower such as the United States, he argued, should not try to impose its rule on all continents but should intervene only when another major power threatens to rule a region of strategic importance. Mearsheimer thus judged U.S. participation in World War II to have been entirely appropriate, since Nazi Germany and imperial Japan sought to dominate their respective regions. However, he criticized post-Cold War U.S. foreign policy for overestimating the country’s military power and its capacity to project that power at will. Mearsheimer notably advocated the withdrawal of all U.S. forces from Europe, arguing that their presence there was irrational, as no state currently threatened to dominate the continent.
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In 2007 Mearsheimer coauthored with Stephen M. Walt a best-selling but highly controversial book, The Israel Lobby and U.S. Foreign Policy (2007). It contended that a powerful lobby skews U.S. foreign policy against the country’s national interests by securing unconditional support for Israel. Some decried the work as conspiratorial or factually weak, whereas others applauded its authors for having the courage to raise an important policy issue.
Mearsheimer’s other works included Conventional Deterrence (1983), Liddell Hart and the Weight of History (1988), Why Leaders Lie: The Truth About Lying in International Politics (2011), The Great Delusion: Liberal Dreams and International Realities (2018), and scores of articles published in academic journals. He also frequently participated in public debates by contributing op-ed articles to the The New York Times and other national newspapers. In 2003 he was elected to the American Academy of Arts and Sciences.