The theme of this clearly and convincingly argued book is that, however disorderly the rest of the world may be, "there was, and is, a new security order in Europe," which represents "the dawn of peace" there -- even if it cannot do much about internal violence. With the end of the Soviet empire, the return of democracy -- albeit fragile -- in Eastern Europe, and the military balance that prevails on the continent thanks to the "treaty-imposed restraints" that all European states have accepted, an almost unprecedented common security order is now in place. NATO plays a major role in this order but would jeopardize the "best of all possible worlds" by "either the contraction or the expansion of its membership." The strength of the argument lies not only in Mandelbaum's skillful demonstration of it, but also in his careful analysis of the agreements negotiated in the 1980s and 1990s and the way they have contributed to NATO's "defense dominance." Mandelbaum's critique of NATO expansion remains as trenchant and sensible as it was when he presented it last year. As for Russia, he argues, rightly, that its future will largely be determined by internal developments, but adds that a continuing American military engagement in NATO will play an important role in preventing Russia from becoming a source of European instability once again.