It is often difficult to know who the "good guys" and "bad guys" are. Many times wars involve bad guys fighting bad guys. Secular governments usually struggle to decide whether or not to get involved (unless they have been attacked directly). Individuals face this same dilemma. This is because wars are usually not black and white, good versus evil in nature.
World War I is a great example of the murkiness of war. Europe had managed to make it through the 1800's without any major conflict. This was a great blessing from God. Unfortunately, by the early 1900's few people remained alive who remembered the horrors of war. Additionally, the industrial revolution had brought about new weapons that many in the military wanted to try out. Because of all this (and many other factors), saber rattling began. All it took was Archduke Ferdinand's assassination to unleash warfare like no one had ever seen before.
Who were the "good guys" in World War I? The answer is that there weren't any. This is how we, as followers of Christ, should think about war. The vast majority of the time wars are not good versus evil, but evil versus evil (or at least more evil versus less evil).
This brings us to the one more reason why World War II was such a travesty. On the surface the second World War looks like a clear-cut decision. There were really bad guys who had to be stopped, and we good guys were going to stop them. Hitler attacked, so we attacked back. Japan bombed Pearl Harbor, so we nuked them (twice no less!). We were good, and they were bad. End of story.
I believe that Christians should not have been involved in World War II, at least as far as killing goes. However, for the purposes of this post I just want to point out one thing: the additional travesty of World War II is that many within the church still think of all wars as being the World War II type: clear cut good against evil. This thinking, in turn, leads the church (ironically and tragically) to be one of the biggest supporters of the military when we go to war.
If we look at U.S. warfare post World War II we see a murky quagmire. The good versus evil thinking fails when looking at Korea and Vietnam. Were we (the U.S.) really with the good guys? Were there any good guys? What if we were the bad guys?
The first Persian Gulf war seems to be fairly clear cut as wars go. However, our involvement there has led to all sorts of terrible ramifications since (such as the 1993 and 2001 bombings of the World Trade Center). Wars always have unforeseen, negative consequences (see the far too harsh Versailles Treaty that ended World War I and its leading to the rise of Nazism in Germany).
America's involvement in Afghanistan and Iraq post 9/11 has been an absolute disaster in almost every way possible. We've lost hundreds of soldiers, killed thousands of civilians, spent billions of dollars, and left both situations in worse shape than before we arrived. And this makes us the good guys? I don't see how.
Wars are murky. We ought to think of them as they are: much more like World War I than World War II. Additionally, we Christians are members of a far better kingdom: our citizenship is in heaven. Why then would we followers of the Prince of Peace ever kill on behalf of a secular government? We do far better to abstain from warfare as it rages around us.
Let's be people of peace, not war.