Final answer:
The ethics of a nation going to war can be evaluated through the Just-War theory, considering defense, deterrence, and proportionality of harm. However, Normative Relativism suggests that views on the morality of war vary across societies. Contemporary warfare against transnational threats introduces new ethical questions about sovereignty and civilian impact.
Step-by-step explanation:
When considering the ethics of a nation going to war, the Just-War theory provides a framework by which to judge the morality of such actions. Wars may be considered ethical when they are in defense or deterrence and the harm inflicted is proportional to the good achieved. A significant point is whether the evaluation of the war's justification should include the total harm done or only the prospective harm. For example, using preemption, the United States has historically involved itself militarily only when threatened, suggesting a war is more justifiable under the threat of imminent harm to its security or interests, as seen in the U.S. campaigns against communism or the Iraq War of 2003.
Furthermore, the moral duty of a state to protect its citizens may lead it to war under certain circumstances, such as when there is a material impossibility to further sustain peacetime in the face of an offensive alliance of stronger enemies, or when one nation's aggression threatens the sovereignty of another, invoking the Munich Analogy. However, it's essential to consider Normative Relativism, which suggests that ethics and morality are social constructs, and the perception of whether a war is ethical can differ significantly across cultures and societies.
Lastly, modern challenges in foreign policy, such as combating transnational threats like terrorism or climate change, have led to unconventional warfare tactics like drone strikes, which raise new ethical considerations in terms of sovereignty and collateral damage.