What is the difference between classical deterrence theory and modern deterrence theory?

The purpose of deterrence is to prevent war. Let us assume that a potential aggressor is showing signs of an armed attack, such as mobilizing troops and deploying them to the border. In this case, the targeted defender can hope to discourage the aggressor from carrying out the armed attack by signaling that it is prepared to fight to the end against any such attack and that it can inflict significant losses on the enemy.

As the costs a state incurs in war decrease, the expected benefits it can gain from war increase. In theory, if one side possesses overwhelming military power and the other possesses only weak military power, it is predicted that war will be more likely to occur because the resistance the aggressor would face if war were to break out is presumed to be minimal, keeping costs low.

I believe this is an argument that is probably generally known. In policy debates in Japan, this type of deterrence theory is often used to explain how much defense capability is needed and what kind of equipment is required. While it is true that this theory can sometimes explain the success or failure of deterrence, it is also important to know that because it is a deterrence theory constructed during the Cold War, it has various limitations and challenges, and it is an argument that is being weeded out in academia. The deterrence theory supported by modern researchers does not focus solely on military capabilities like classical deterrence theory.

Each country's expected outcome of war differs

First, in military affairs, evaluations of the superiority or inferiority of military power often differ significantly. The elements that constitute military power are diverse and are not of a nature that can be measured simply by quantitatively measuring the scale of human and material resources. Rather, it is understood that the important elements of military power are those that cannot be measured objectively, and it is believed that the results change significantly depending on how units are organized and how they are operated.

Classical deterrence theory assumes that the relative superiority or inferiority of military power is self-evident and that there is a common prediction about what might happen if a war were to occur. However, in reality, the information available to policymakers in both countries when making such predictions is extremely incomplete, and just because one side is confident of victory does not mean the other side is prepared for defeat. Even if the disparity in military power is clear, it is entirely possible for both sides to be confident of victory at the same time.

In fact, when investigating the state of the military balance when past wars occurred, it has been found that war is more likely to occur when the superiority or inferiority of military power is unclear and evenly matched than when there is a clear disparity in the military power of the two countries. Therefore, modern deterrence theory considers that deterrence is more likely to fail when both countries make different predictions about the possible outcomes if a war were to break out. However, once a war begins, the results of the fighting allow both sides to obtain accurate information about the superiority or inferiority of their military power. It should also be noted that such sharing of information regarding the strength of both sides can be a factor in promoting peace.

Anxiety and fear about the future lead to preventive war

Returning to deterrence theory, it has now become well known that anxiety and fear that one's own country might be placed in a position of military inferiority in the future make deterrence difficult. This is a risk that intensifies when military buildup is progressing in various parts of the international community, including one's own country.

For example, if a country notices that a neighboring country's military buildup is rapidly expanding, it may fear that those armaments will eventually be used against it. If it perceives such a threat, the country may think it would be better to attack before the neighbor advances its military buildup any further. Launching a war with the expectation that it will become a threat in the future in this way is called a preventive war in strategic terminology.

Modern deterrence theory actively incorporates the findings of psychology, and there is a finding that people who feel anxious about the future are more likely to excessively perceive the hostility of those around them. Since national leaders are also ordinary human beings, if they feel fear that their country will be in a military predicament in the future, it affects their social cognition, and even if the neighboring country actually only has defensive intentions, they are more likely to misidentify them as having aggressive intentions. Such misidentification can be a cause of preventive war.

Also, political psychology has shown that in order to maintain power domestically, leaders may take an unnecessarily hardline stance against foreign countries to gather broad support from the public. Leaders with such motivations are more likely to underestimate the enemy's capabilities and overestimate their own. If such cognitive distortions worsen and they become unable to process information accurately, even if they try to bridge the gap in positions through diplomacy, it becomes impossible to align both sides' perceptions of the future of the war, and they cannot reach a compromise. This is also a major problem that causes deterrence to fail.

Summary

Modern deterrence theory predicts that the fact that information about the current state and future of the military situation is always incomplete increases the risk of war. Classical deterrence theory assumes that national policymakers use accurate information, calmly judge the level and superiority or inferiority of military power, and choose the optimal response, but that is not a realistic assumption. Policymakers are always perceiving the situation using incomplete information, and there is always a possibility of misunderstanding or misidentifying the intentions and capabilities of neighboring countries.

Therefore, modern deterrence theory emphasizes the importance of diplomatic negotiations as well as military buildup. This is because the more both sides communicate continuously and share information about their intentions and capabilities, the more it can be expected to reduce the risk of war. However, if politicians have acquired bellicose beliefs or are taking a proactive stance toward war due to domestic circumstances, the effects of deterrence cannot be expected even if efforts are repeated in diplomacy. In such cases, it is necessary to convey that we are also armed and to send a message that if an attack is carried out, we will use every military means at our disposal to inflict massive damage on the opponent.

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