Mearsheimer boldly states that great-power rivalry is not over. The major powers still fear each other, and dangerous security competition lurks. This view is built on an "offensive realist" theory of world politics: the deep insecurity generated by the anarchic (hence "tragic") international system leads great powers to act aggressively toward each other, thwarting rivals from gaining power even if such moves risk war. Moreover, great powers are rarely satisfied with the status quo and instead seek hegemony. Mearsheimer tests his theory across the last two centuries, citing the territorial conquests of Japan and Germany before 1945 and Soviet policies after 1917 as evidence. The United States and the United Kingdom do not fit as well into Mearsheimer's framework, but he argues that the "offshore balancing" strategies of these maritime states are just more sophisticated versions of calculated aggression. As a result, Mearsheimer predicts, the post-Cold War peace among great powers will soon end: without a peer competitor in Europe or Asia, the United States will retract its security commitments there and great-power security competition will return. But he does not make clear why the United States would act in this way -- even if it is a sophisticated power maximizer.