The existence of alliances between unequal states is a puzzling one. Major powers appear to gain little in terms of security from allying with minor powers, while minor powers live in fear of being abandoned by their major power patrons. However, as Morrow (1991) theorized, major states gain some autonomy benefits from such alliances, while the minor power(s) in the alliance gain security. In this dissertation I conceptualize extended deterrence as a benefit that great power defenders proffer to minor power allies. Major powers are able to receive benefits from their minor power allies that permit the major powers to maintain a global presence. Minor powers gain security from this relationship, with the major power's capabilities enhancing the deterrent aspect of the alliance.;I maintain that the credibility of such a deterrence commitment can be developed if the great power defender uses costly signals as a means of demonstrating their commitment to their ally's defense. These costly signals serve as investments made by the great power into the minor power. These investments provide cues to potential aggressors, and serve as indicators of how committed a defender is to protecting an ally. These investments are conceptualized in this dissertation as security benefits provided by the great power defender. In return, the great power defender must receive some benefit for its provision of security. I maintain that the autonomy benefits the protege is willing to sacrifice in return for gaining security also send signals to a potential attacker, and help determine the value that a defender has for its protege;Within the general framework of security/autonomy I construct a signaling model of extended deterrence via alliance. I argue that perceptions about the strength of the defender's signal determine whether an aggressor state makes a demand of a great power's protege. I empirically test hypotheses derived from the signaling model on a set of alliances drawn from the nineteenth and twentieth centuries. Each of these alliances has some deterrence component explicated in the reason for its existence. I utilize a bivariate probit with selection to analyze data pertaining to signal strength, benefits derived for the major power, the balance of forces, domestic costs, and international reputation costs. I analyze both extended general and extended immediate deterrence, both as individual equations and as part of a larger, sequential process. I find that changes in the strategic environment play a role in determining whether extended general deterrence succeeds or fails. This is largely a function of the investment of time and money that the defender has made in the relationship. At the level of extended immediate deterrence I demonstrate that great power defenders are more likely to intervene if major autonomy benefits are threatened. This holds even if the defender is weaker than the challenging state. The findings of the dissertation suggest that alliances are better at deterring aggression than has previously been assumed, and that if enough costs are invested into the alliance, they tend to be more reliable.
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