Jim Webb, writing in these pages several years ago, castigated the U.S. Congress for its unwillingness to take up its Constitutionally-mandated responsibilities to conduct vigorous oversight of American foreign policy. Future historians are likely to add to his bill of particulars the Senate providing a rubber stamp to the several rounds of enlargement of the North Atlantic alliance, without weighing the costs and obligations of willy-nilly extending U.S. security guarantees.

When the Washington Treaty creating the NATO alliance was presented to the Senate in 1949 for ratification, there was a vigorous debate over its utility. As C. L. Sulzberger chronicled in his contemporaneous reporting for the New York Times, Senate approval of the pact was neither foreordained nor automatic. In the end, many Senators reluctantly cast votes in favor in order to send a clear signal to Josef Stalin that the United States would actively resist Soviet aggression, but the arguments marshalled by Senator Robert Taft nonetheless fell on sympathetic ears in the chamber (and convinced twelve others to join him in voting against the treaty).

Taft had argued that the U.S. should have extended unilateral security guarantees only, rather than sign a treaty of alliance, because “We could judge whether perhaps one of the countries had given cause for the attack. Only Congress could declare a war in pursuance of the doctrine.” Taft enunciated concerns that the new alliance might shift from defensive purposes to a more active encirclement of the Soviet Union, and so provoke the war it sought to prevent. He also raised a more prosaic concern: that of free-riding on the part of allies who might grow dependent on U.S. largesse rather than take more steps to secure their own defense.

Because of the extended debate in the Senate, the members of the upper house heard, weighed, and assessed Taft’s objections, and most rejected them, taking the position that the security of the United States would be better protected by investing in the alliance and accepting the obligations of Article 5 of the Washington Treaty that an attack on one would be considered an attack on all. This helped to create an enduring bipartisan consensus even when control of the White House and of the Congress shifted back and forth between the parties. Most importantly, the Washington foreign-policy community made clear, compelling and persuasive arguments to “Main Street” that protecting allies in Europe was directly and intimately connected to the security and prosperity of the average American.

For most Americans, the perceived utility of the NATO alliance declined with the collapse of the Soviet Union in 1991. Anxious for a peace dividend, the general public was susceptible to the siren call for America to “come home.” The strategy of “democratic enlargement” was meant to replace containment of the Soviet Union as the principal justification for continued American engagement around the world, not by focusing on an existential threat to the homeland, but about the increased benefits that would accrue to Americans—a growing number of partners who would assume more of the burdens previously shouldered by the United States while expanding markets for American goods and services.

Yet it was not immediately obvious after the collapse of the USSR that a strategy of democratic enlargement would require the expansion of the NATO alliance to encompass new members from the states of the former Soviet bloc. Certainly no one headed the scattered calls for dissolving the alliance at the end of the Cold War, because the organization remained a pillar of Western European security and an important part of the U.S. national-security toolbox. But the initial proposals to reassure the democratizing states of central and eastern Europe that had just escaped from the Soviet bloc focused on security cooperation efforts and sets of guarantees. It seemed that the argument Taft lost in 1949 might prevail in the 1990s: the United States would offer its own defensive commitments, but in a manner that would give Washington a great deal of freedom of assessment and action. This would prevent it from being drawn into situations that enhanced neither U.S. interests nor U.S. security, or that risked a possible clash with a post-Soviet Russia by locking the United States into automatically taking the side of Russia's neighbors in the event of any dispute (over borders, the status and treatment of minority groups, and so on).

That perspective began to shift within the Clinton administration, driven in part by concerns that the new democracies of the east needed to be anchored as formal members of NATO and by their historical fears of being caught again on the wrong side of any future dividing lines in Europe. Thus, in September 1994, then vice president Al Gore noted: “Everyone realizes that a military alliance, when faced with a fundamental change in the threat for which it was founded, either must define a convincing new rationale or become decrepit. Everyone knows that economic and political organizations tailored for a divided continent must now adapt to new circumstances-including acceptance of new members-or be exposed as mere bastions of privilege.” Expansion would provide a new rationale for NATO's existence in place of containing a Soviet threat.

But a dangerous set of paradoxes was introduced into the approach for post-Cold War NATO enlargement. On the one hand, the argument put forward, first by the Clinton, then by the Bush administration, was that the states of central and eastern Europe needed to be admitted to the alliance because remaining outside the alliance would leave them insecure and vulnerable. On the other hand, the U.S. maintained that binding security guarantees could be extended to these countries without taking on any new risk because there was no conceivable major security threat that might require those guarantees to be enforced. Post-Soviet Russia was either assumed to be finished as a great power, on track for its own eventual accession to NATO, or could be persuaded by Washington not to see NATO as a problem. Increasing the number of countries and the geographic area where the United States would now be contractually obligated to view an attack as an attack on the U.S. homeland was not a cause for concern because the experts were confidently predicting that no circumstances could be envisioned under which those guarantees would ever need to be invoked. Somehow, NATO enlargement was supposed to eliminate any possible causes of conflict in eastern Europe, especially between those anticipated new members that shared direct borders with Russia, so that there would be no need for the U.S. to worry about being drawn back into conflict in Europe. Moreover, expanding the number of members was supposed to result in even greater burden sharing, with the alliance transforming itself, as Senator Richard Lugar stated during the April 2003 hearings on enlargement, “into an important force in the war on terrorism”—with NATO members increasingly and enthusiastically providing forces and equipment for so-called “out of area” operations.

Unlike in the 1940s, no modern equivalent of Taft rose in the well of the Senate to pose hard and tough questions about enlargement, its costs and its risks. During the first round—to admit Poland, Hungary and the Czech Republic—there were concerns raised about whether the candidate countries might relapse into authoritarian nationalism and so provoke conflict (especially in reference to developments at the time in Hungary and the possibility of NATO becoming involved in clashes over territory and borders between eastern Europe members and nonmembers, such as a Hungarian clash with Romania over Transylvania). Such concerns did lead a few Senators to vote against enlargement—but for the most part such heretical thoughts against the faith in the irreversible linear progression of democratization were squashed, because the concurrent expansion of both NATO and the EU would render things like illiberal nationalism a thing of the past.

Taft-style concerns then became seen as anachronisms. Expansion was seen as having no downsides for the United States. In legislative actions such as the resolution proposed by Representative John Shimkus in the 107th Congress (and adopted by a voice vote), the idea that future NATO members should be assessed by criteria such as the benefits their joining the alliance would bring to enhancing U.S. security were set aside by the proviso that countries like the Baltic States (and later, Ukraine and Georgia) should be given invitations to join if they so desired and met the technical standards for NATO membership. In other words, it was up to the new applicants to decide whether they wanted to join, not for the United States to decide whether giving binding security guarantees was in U.S. interests. The second “big bang” wave of accessions to NATO—including U.S. ratifications of Article 5 guarantees for the Baltic States—passed the Senate on May 8, 2003, with 96 votes in favor (and none cast in opposition). Seven countries—some with deep historical rivalries with other NATO members, others who had ongoing, unresolved issues with Russia—were admitted.

In the immediate years after enlargement, potential volcanoes remained dormant. In times of European plenty, the European Union had a good deal of leverage to tap down any flareups of nationalist irredentism, to coax governments to do more to accommodate their national and linguistic minorities, and to forestall slides into illiberalism. Russia was only beginning its revival after the post-Soviet collapse and there was yet confidence that new dialogues with the U.S. and the Europeans might yet find a way for Russia to have a substantive voice in European security affairs.