them. At the beginning, many Warsaw Pact countries took directives from Moscow in part because the local presence of commissars and the Red Army had an outsized impact on local domestic politics (see Rice 1984). Geography is not destiny.
There are, of course, benefits in allying with a weaker state. The example of the Soviet bloc suggests how political control over domestic and foreign policy can be one such benefit, but again such control is often incomplete and can dissipate over time (Cooley and Spruyt 2009). A second benefit is to acquire so-called defense-in-depth. In military parlance, defense-in-depth refers to a strategy where an attacker must confront successively robust layers of defensive points designed to absorb the first blow, delay the attacker’s forces, and buy time for the defender to respond. A third, cruder benefit is that allies can be buffer states if they provide a battleground away from the territory of the great power where fighting with the adversary will first take place. The Soviet presence in East Germany and Poland offered Moscow this defense-in-depth against Western Europe, which it did not really have prior to the Second World War. Still, a defense-in-depth strategy or a buffer zone is no good if allies wrangle with each other. In cases where allies have a history of acrimonious relations with one another, extending security guarantees to each of them can help diffuse tensions by reassuring them both that their interests are heeded. The US military presence in Europe has, arguably, had this stabilizing effect. By becoming a European power in its own right during the Cold War, the United States inserted itself between France and West Germany, allaying concerns that the historical antagonisms they had for each other could resurface and would lead each to take up their disputes with military force again.
A fourth possible benefit to military alliances is that they facilitate such military cooperation as joint military exercises, interoperability, and personnel exchanges. Military alliances are not entirely necessary in order to create this particular benefit, but they can provide an institutional foundation for their continuous and regular operation. True interoperability requires reducing uncertainty and so can benefit from technological transfers, unified command systems, intelligence sharing, and other cooperative endeavors that allies would not consider doing for those that they fear would almost certainly renege on their pledges. Of course, these institutional foundations may or may not be of service if the great power needs to cobble together a coalition of states to undertake a military campaign. As Chapter 5 highlights, major problems of interoperability can persist and hamper those military operations that even longstanding allies undertake. Finally, having an ally on one side may in some cases be better than having it in the enemy’s camp. For example, the ally might be positioned near key waterways or other sites of strategic interest that could be useful for projecting power in a wartime situation. Turkey has been consistently valuable to NATO precisely because of its location vis-à-vis the Dardanelles and the Bosporus. Put together, it is unclear whether great powers really do give up their security to weaker states if such arrangements can augment their sense of security as well.
A version of the concession-extraction argument holds that alliance formation can result from an expansionist foreign policy that is pursued for its own sake. This sort of argument has gained currency in recent years among those critics of US foreign policy who allege that Washington has taken on too many alliance commitments as part of a global liberal crusade or hegemonic project (Posen 2014; Mearsheimer 2018). Allies might not necessarily have made concessions, to be sure, but alliances still serve to project influence in the pursuit of a grand ideological initiative. As an explanation for alliance formation, this thesis overlooks how the United States has been uneven in advancing liberalism abroad (Jervis 2020: 18–19). After all, Taiwan is a successful liberal democracy but receives no such treaty commitment from the United States despite Taipei’s eagerness to have one. Nevertheless, it is possible that the United States emerged from the Cold War victorious and with so much power that it sought to exploit the situation by trying to widen its authority even more (Mearsheimer 2018). Again, if Washington aimed at achieving global hegemony, then the willingness of small states to jump on that bandwagon rather than oppose it still requires explanation. Part of the answer may be that, for democratic states especially, the United States is an attractive partner because its democratic constitution and willingness to use international institutions, however selective this may occasionally be, make it less likely to dominate other states (Ikenberry 2001). But even this explanation is incomplete. Not only should the United States be nonthreatening to potential allies, but, as the previous discussion suggests, those potential allies should likely perceive to some degree the same threats that the United States perceives.
But Why Have an Alliance Treaty?
A major weakness of both sets of arguments discussed above – that alliances are formed to face threats and help states to extract small power concessions (and thus to gain influence) – is that they leave unexplained the existence of a treaty. States can collaborate in face of a threat without having to sign a treaty. Alarmed by Iran, the countries of Israel and Saudi Arabia have improved their ties despite the historical animosity that they felt for one another. Their security personnel and their defense officials have met on multiple occasions. Saudi Arabia has apparently signaled its “willingness to provide Israel an air corridor and air bases for rescue helicopters, tanker aircraft and drones in case Israel decided to bomb the Iranian nuclear facility” (Abadi 2019: 444). No alliance seems probable between them, however. Similarly, uneasy about the rise of China, Vietnam has signed memoranda of understanding and enhanced defense cooperation with Australia and Japan, but has so far not signed an alliance treaty with either (Liff 2016: 450). In the book in which he advances the theory that states forge alliances to balance threats, Walt (1987) considers both formal treaty alliances and informal alignments. As I highlight in Chapter 5, many coalitions of states have been formed in wartime and fought effectively against their adversaries, despite not having an alliance treaty beforehand. Leaders of states should just as easily be able to communicate their intention to stand firm against an adversary through public statements. In this vein, US President Franklin Delano Roosevelt pledged to defend Canada in a thinly veiled reference to Nazi Germany when he accepted an honorary doctorate at Queen’s University in Kingston, Ontario, in 1938 (Granatstein 2020: 145).
Strong states should not have to sign treaties if they wish to extract concessions from smaller states. They should be able to do so by dint of their strength alone, in keeping with the oft-repeated notion that “the strong do what they can and the weak suffer as they must.” Strong states presumably have options other than alliance commitment if they wish to safeguard another state from external attack. As the United States did with Saudi Arabia between the 1990–1 Gulf War and 2003, a great power can station its forces on the partner’s territory in the absence of an alliance treaty. Another option is to provide security assistance. This can involve the transfer of weapons, especially those that are largely defensive in character so as to lower the risk of the recipient starting an unwanted war of its own. The United States decided against extending a treaty commitment to Israel in the 1960s and the 1970s, but stepped up its arms transfers in part to ensure that Israel would not be outmatched by its Arab rivals. Not long after abrogating a treaty alliance with Taiwan in 1979, the United States supplied it with weapons as a means of deterring China from launching an assault across the strait (see Yarhi-Milo et al. 2016). As former Assistant Secretary of State for Political-Military Affairs Andrew Shapiro once remarked, “[w]hen a country acquires an advanced US defense system, they are not simply buying a product to enhance their security, they are also seeking a relationship with the United States” (2012: 20).
International relations scholar James Morrow (2000) argues that states write down their alliances because doing so serves to signal commitment. Recall how “defensive alliances” really aim to deter war rather than to fight a war on the defensive. But to deter a war, a state, or a group thereof, must communicate to its adversary which actions are unacceptable, what consequences would follow if those actions are undertaken, and, significantly, how resolved it is to follow through on imposing those consequences, provided that it has the will and capacity to do so. One prerequisite to deterrence is assurance: the notion that promises will be kept and good behavior will not be
