Abstract: Realist alliance theory predicts that U.S. security guarantees to its allies have been weakened by the disappearance of a common enemy. But German and Japanese balancing efforts against future threats are likely to be impeded by their antimilitarist cultures and institutions. The resultant over-reliance on U.S. protection would undermine deterrence, and would postpone German and Japanese efforts to acquire nuclear weapons until a serious crisis develops, though this would be a dangerous time to go nuclear. The severity of this problem is difficult to assess, due to uncertainties in cultural and institutional theory and about how future great power conflicts may develop. But the over-reliance problem suggests at the least that the alliances are not as peace-causing as is often claimed, and that more attention ought to be paid to regional or independent security alternatives for Germany and Japan.