In continuing the discussion of ethics in war, I want to now focus on the decision to enter war. War by definition causes loss of life, usually both civilian and military. So when is it justifiable, and when is it not?
I initially looked for a definition to post for why a country has a military to begin with, but definitions available are either vague (e.g. webster's) or uncited (e.g. wikipedia). Given that, all that follows is from my head, so feel free to disagree as you see fit.
Almost every country has a military of some sort, with the number 1 goal of protecting it's people from outside attackers. Thus, there's usually a Department of Defense or such put in charge. So, if a country is attacked by invading forces on its sovereign territory, it seems necessary to engage in war to defend itself. Yet this is only a clear cut decision when there's an immediate threat on your home turf that must be stopped, with a recognizable foreign army playing by a set of international rules. What happens when you're attacked on foreign soil, such has been the case with embassy bombings of the US throughout the world? If you're being attacked sporadically, does it still count as an imminent threat? And if you knew your country was going to be attacked tomorrow, would it be morally justifiable to preemptively strike?
Now, there's also the diplomatic approach to solving conflict, without engaging in an all out war. Obviously, diplomacy takes fewer lives than war, and thus a quick diplomatic solution would be preferable. Yet in the case of an invading army, talking will do little if they gain control of your cities. In the case of isolated attacks, how long does one hold off military response while pursuing diplomatic pressure? Even in negotiations, prior military restraint might decrease your country's standing and thus negotiating ability. Depending on the point in history and location in the world, willingness to negotiate may be seen as a strength or a weakness. Additionally, if your "enemy's" goal is to destroy your country, can you really even negotiate?
Lastly, when living in a country with one of the world's strongest military powers, don't we have a responsibility to use our might to protect those who cannot defend themselves? With genocides in Rwanda, Darfur, etc, one might see us obligated to be engaged around the world, as a moral police force of sorts, even though it risks the lives of our citizens. If we take this premise of moral responsibility, yet the need for our intervention exceeds our ability, how do we decide where to deploy our soldiers? In deciding between two equally justified engagements, is it ethical to be selfish and choose the one that might bring financial benefit to us? Or does that cross the line of risking our lives for financial gain?