The question of whether war is a rational act of state policy is a complex one, and opinions differ on the matter. While some argue that war can be a rational tool of state policy, others contend that it is often driven by irrational factors, such as ideology, nationalism, and emotion.
In the 20th century, there were numerous wars that were fought for a variety of reasons, including territorial disputes, resource competition, and ideological conflicts. Some of these wars, such as World War II, were arguably fought for rational reasons, such as the desire to protect national security or expand territory. However, even in these cases, the decision to go to war was often influenced by irrational factors, such as the ideologies of the leaders involved or the desire for revenge.
Other wars of the 20th century, such as the Vietnam War or the Soviet-Afghan War, were more clearly driven by irrational factors, such as the desire to spread ideology or maintain political power. In these cases, the decision to go to war was often not based on a rational assessment of the costs and benefits, but rather on political considerations and the desire to maintain power.
Overall, while it is possible to argue that war can be a rational act of state policy, the history of the 20th century shows that wars are often driven by irrational factors and can have catastrophic consequences. Therefore, the decision to go to war should always be made with great caution and after a thorough analysis of the costs and benefits.