In order to understand the role of the rational choice and balance of power theories in international relations it is useful to consider the world as an anarchical arena in which every state holds full sovereignty and is independent in taking political decisions. Unlike the relations within the state among different political institutions and actors, in the international relations it does not exist a hierarchy of powers nor is there a supreme binding judicial body that may syndicate on the respect of international law or punish the transgressors of it. Let us remember, for instance, that the International Court of Justice can have jurisdiction over a case only if the involved actors agree. In truth, the international relations are the consequence of particularistic and opportunistic considerations oriented toward the augmentation of national prestige, power and welfare.
In this context, the theory of rational choice plays a key role. This theory, albeit borrowed from economics, states within the international relations that an actor attempts to achieve the greatest possible benefit with the lower costs: in other words, it is convenient to do nothing else but pursue the greater good, avoid the greater evil, or at least, to settle for the lesser evil or good.
Economists often apply to the principle of rational choice. The basic idea that upholds the theory is to confront all the costs and benefits of a given activity. Considering an enterprise or a consumer it is a reasonable and rational decision that makes them decide in the former case which outputs to produce and how many of them, and what to purchase according to the own income in the latter. In this sense, the rational decision implies the choice, amongst different available alternatives, of the one that gives a major benefit in relation to the cost. Moreover, in economics rational choices imply the contemplation of marginal costs and marginal benefits, namely the variation of costs and benefits that occur in doing a certain activity in a slightly superior or inferior quantity than a given level: marginal costs/benefits should thus be considered separately from the total costs/benefits of a given activity. Ultimately, we can summarize the idea of rational decision by affirming that it implies the confrontation between marginal benefits and costs: whether the marginal benefit is superior to the marginal cost, then it is rational to start or to expand a certain activity; whether instead it is inferior, it is rational not to begin it or to diminish it. Applying the theory to the theoretical principles of international collaboration, it represents the model through which international alliances and foreign policies choices are conceived and developed. The calculation of the (marginal) costs and benefits of an offensive or defensive alliance, the right granted to foreign troops to transit over a land, the conclusion of trade agreements, and any other form of negotiation wholly rely on realistic and strategic analyzes that see in international interaction a range of opportunities that can be more or less profitable.
Now, one of the consequences of an international order that applies on equal terms the theory of rational choice is the consolidation of territorial stability following the principles of the balance of power. Wrought by English policymakers and strategists, the principle of the balance of power was typically characteristic of the eighteenth century, and it finally affirmed in the European continent during the nineteenth century after the Restoration. The balance of power is one of the key concepts of realist thought and refers to that condition in which political leaders manage to avoid or suspend the natural propensity to war by mutually fostering a kind of balance that equilibrates their geopolitical weight. This would lead to the making of a stable and ordered international system that could overcome international anarchy.
In order to achieve the balance of power, there are two main strategies, albeit complementary, to implement:
1) Make sure that the power of a stronger political entity, such as an empire, is reduced in order to rebalance its relevance in favor of lesser political entities.
2) Increase the power of the weaker political actor in order to resize the gap of power towards the other actors of the international system with which it interacts.
In practice, these strategies contemplate four different mechanisms aimed at achieving international balance:
1) Divide et impera: it consists in avoiding the creation of excessively strong coalitions, and in pursuing the annihilation of powerful alliances that either already exist or are being created. The existence of extremely forceful political poles makes it more demanding to conceive counter-balancing strategies.
2) Compensations and territorial partition: this avoids the possibility that a single actor manages to take possession of an excessive quantity of resources and lands, and it helps to compensate the disadvantages that affect the weaker actors of the international system.
3) Dissuasive strategies: consisting in the implementation of policies liable to deter other players of the system from falling prey to greed and lust of conquest, and thus in making choices that can threaten the territorial integrity and survival of the weakest actors, with the risk of unbalancing and altering the international system.
4) Calculated alliances: The aim consists in benefiting from a mechanism that allows fast shifts of the weights, counterweights and powers within the system. This mechanism works best when there is a country that can play the role of balancer for the fact of being in a relatively independent position than other players. The balancer should also be strong enough to be able to intervene in the game of alliances, redistributing the political weights through appropriate choices and in considering mandatory the need of preserving the balance of power.
In fact, these mechanisms require two different tools to find concrete application: war and diplomacy. Moreover, the political entities that are able to implement these strategies are inevitably those who are either already sufficiently mighty to impose their will on others, or those that, having won a war or a military campaign, have gained a political superiority over the others that allows them to dictate their conditions at the negotiations for peace. In the latter case, the relevance of the winner’s will depends on the importance and degree of the attained victory. So, as it is true that winners write history, it is equally true that winners are those that establish a balance of power that is compatible and, where possible, convergent with their geopolitical strategies.
Indeed, the theory of the balance of power entails several problematic issues. Generally, since the objective power of international actors is difficult to evaluate, it is complex to estimate when a system actually reaches the condition of equilibrium of powers. It is also difficult to calculate the effectivity of the ties that bind a coalition, because alliances are as easy to create as to terminate, and thus it could be dangerous to rely on them as guarantors for a state’s security or for the endurance of the system’s equilibrium. Furthermore, the balance of power international arrangement works better only in the case that all the actors of the system possess common norms and values, so that they will be able to appreciate in a comparable condition the common strategies that lead to the systemic equilibrium.
According to Kaplan, the balance of power system is able to work properly only when some minimal conditions occur: the existence of a minimal number of actors, the absence of radical ideological and religious contrasts, the goodwill of the actors to respect the rules that the system implies, and a “providential” intervention of a kind of “invisible hand” that guides the actors’ decision, similar to the one that according to Adam Smith would guide free market.
In addition, Morgenthau attributes four different meanings to the concept of balance of power based on the emphasis of different aspects related to it: according to the situational aspect, the balance of power is a policy aimed at obtaining a given situation or status quo; for the objective aspect, the balance of power indicates an effective and “real” condition; for the equilibrating aspect, it is a system that tends to reach a homogeneous and equal distribution of power; finally, according to the distributive aspect, balance of power means the presence of a mechanism of power transfer, i.e. an automatic mechanism that generates power redistribution.
At the same time, Wight, the founder of the so-called “English School”, highlights some alternative definitions to the notion of balance of power: the classical definition of balance of power suggests that the international actors share out power in a homogenous fashion; the normative definition considers the balance of power as a general rule that enounces a principle of equilibrium that ought to be uphold in order to grant an optimal function of the system; and an attitudinal definition by which the international system naturally and instinctively tends to establish a balance of power amongst its actors.
Finally, K. Waltz, the chief theorist of neorealism, underlines the structural-systemic origin of the balance of power, highlighting how in an innate anarchical international system the principle of balance of power serves the purpose of self-conserving and self-defending the single actors. In this context, the balance of power is the natural result of the actors’ interaction that operates within the international anarchical system and of the natural competition due to the unequal distribution of power, which undermines global safety. Thus, states generate the balance of power not by their own choice, but because, being programmed to survive, they are naturally compelled to gather with others in a balanced coalition that may face the threat of other similar globally spread coalitions of power. In other words, the balance of power is the meeting point between the need for states to grant their own safety and survival and the will to maintain a “relative advantage” in terms of powerfulness. Practically speaking, states determine their own balance of power both by increasing their inner economic, political and strategic capabilities and by strengthening their systems of alliance and weakening those of the rivals. Waltz believes that since the balance of power is the logic result of the structural anarchic international system, all historical periods and international contests have been characterized by it.
Historically, the Peace of Lodi (1454) offers the first paradigmatic example of a balance of power system. Likewise, the Peace of Westphalia (1648) and the Peace of Vienna (1815) offer further examples.
 Sloman, J. (2004). Essentials of economics. Pearson Education Ltd.
 Simon-Belli, C. (2002). Teorie delle relazioni internazionali. Perugia: Guerra.
 Kaplan, M. (1957). System and process in international politics. New York: Wiley.
 Morgenthau, H. (1967). Politics among nations. New York: Knopf.
 Wight, M., Bull, H. and Holbraad, C. (1978). Power politics. New York: Holmes & Meier.
 Waltz, K. (1979). Theory of international politics. Reading, Mass.: Addison-Wesley Pub. Co.