A soldier is about to execute 20 prisoners. He tells you that if you kill one of them, he'll let the other 19 go. This classic standoff between Kantian ethics and utilitarianism is discussed @ "Jim and the Indians" and killing someone to harvest organs, is it equivalent?
Now imagine a vaguely similar situation involving two nations.
Nation A declares war on Nation B, threatening to destroy a city with a population of one million people. To protect itself, Nation B must destroy Nation A's capital, with a population of 200,000.
So either one million people die or 200,000 die.
Of course, this situation is vastly more complicated because we're talking about self-defense as well as political functions - a leader must protect his or her country.
What would a Kantian and a Utilitarian do in this particular situation?
Just for clarification, the soldier in this example is not a liar. We know he's telling the truth. So the exercise boils down to a really simple question: Would you kill one person so that the others could live, or would you stand by and watch the entire group murdered?
Regarding Bread's comment about cities not being the problem, that's literally true - but it misses the point of my question. In my example, there really is no choice but destroy an entire city. If we have to make up a reason, we could say that Nation A has a constitutional clause stating it surrender if it's leader is killed, and it's known that he runs from one hideout to another in the capital city. So the only way to be sure he's eliminated is to destroy the entire city.