Unfortunately, sometimes wars are inevitable. It's all fine and good to say war is immoral. But then, what do you do when faced with lunatic regimes, Kirk?
I'm very receptive to those who argue that there is always the other side of any argument. And I'm always incensed when I see my own government taking questionable positions internationally. But let's be politically correct, using a "safe" example from history, that should offend the fewest number of people. Was the war against Nazi Germany avoidable? If your answer is no, then was it immoral?
Forget the US. Were the Brits justified in defending their islands, or was the "just" course of action to lay down weapons and be invaded? We could use current events as equally good examples. Is it okay for people to shove innocent wheelchair-bound individuals overboard, or throw innocent people off of tall buildings? Or even allowing that some might not consider an utterly nonthreatening person "innocent," even accepting such twisted minds, is it ever okay to let such atrocities happen, especially in cases where they are committed by regimes and not isolated lunatics?
War sometimes is the last resort after long failed negotiation or continous attack from one side even within the same group. In Islam war is exception and verses talk about war come as temporary time قال الله عز وجل :( كُتِبَ عَلَيْكُمُ الْقِتَالُ وَهُوَ كُرْهٌ لَكُمْ وَعَسَى أَنْ تَكْرَهُوا شَيْئًا وَهُوَ خَيْرٌ لَكُمْ وَعَسَى أَنْ تُحِبُّوا شَيْئًا وَهُوَ شَرٌّ لَكُمْ وَاللَّهُ يَعْلَمُ وَأَنْتُمْ لَا تَعْلَمُونَ) البقرة/ 216 .
Fighting has been enjoined upon you while it is hateful to you. But perhaps you hate a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah Knows, while you know not.
War can well be inevitable sometimes, but it can never be just on very simple grounds: it affects the innocent.The very essence of justice is that the guilty parties be held accountable for their deeds, and the the guiltless be treated as such.
Of course, as ever the picture is a bit more complex than meets the eye, because guilt can be direct or indirect and well-hidden. Lack of education and other factors can lead to causes of war in a roundabout way - over resources, over religion, etc. In that case, there might be a level of widespread guilt: this is a free world, and it's incumbent on everyone to educate themselves and act with a measure of wisdom. Failure to do so is in itself a measure of guilt.
But it remains that war places harrowing burdens on people who are totally innocent, on children, on (usually the vast majority of) people who had absolutely nothing at all to do with the circumstances that led to war.
By any definition of justice, war cannot ever be just.
Widely known is the famous saying of Carl von Clausewitz: "War is the continuation of politics by other means". And he was objective right.
For example, the Anglo-Saxons began the First World War to destroy the German, Austrian, Ottoman and Russian empires. And they managed to do it. Then, the Anglo-Saxons brought Hitler to power to unleash the Second World War with the ultimate goal of pushing Germany and the Soviet Union.
And they managed to do it, only the Soviet Union won. In our time, Anglo-Saxons want to push Russia and China, as China became the first economy of the world. For now, the USA wants to destroy North Korea, but it looks like it will be mutual destruction and this fact stops a global war that could be the last war for all the inhabitants of our planet. And lastly, the well-known saying is widely known: "If you want peace, prepare for war." It is thanks to this formula that future wars can be avoided. "Optimists learn English, Pessimists are studying Chinese, but Realists learn the Kalashnikov assault rifle".
War may be needed if there are people or groups of people that are not doing what is best for the rest of the country. There are times when civil war is necessary or times when another country needs to step in and help a majority of people get rid of some one that is threatening what is best.
Several reasons have been provided here for war, at least its toleration, although each equally provides, whether understood or not, means to prevent it. Perhaps that needs to be discussed.
The Nazi example, widely used, rarely considers steps to have prevented its growing power as if its final manifestation was a fait accompli. Interesting that the poor Anglo-Saxons (a mixed group at best) are still blamed for every quirk and historical diversion (invariably complex in origins), while the religious, as always, are the first to take up arms.