You will gain a variety of answers to this question. Some will argue that it is futile because of the massive loss of life and displacement that results from it. Even in the most compelling of wars, the amount of dead and/ or injured, as well as the number of those who are homeless or orphaned as a result are staggering totals. At the same time, an argument can be made that war is futile because it is infinitely regressive and continues on no matter what. Wars are waged and fought and while individuals might believe that a particular war is so bad that it "will end all wars," another one ensues afterwards. I would think that another reason why war is futile would be that the people who die are usually the ones who do not wage it. For example, Elie Wiesel writes, "When adults wage war, children die." In this line, there is much there about who really suffers in wars. The children who die did not authorize or commission the conflict, yet these are the ones who die int he process. This might be another reason why war can be seen as futile.
Saying that war is futile is saying that war is ineffective and pointless and I do not think that this is the case. Like the previous post stated World War II was not futile. We entered this war when Pearl Harbor was attacked. The United States had no choice but to protect itself.
I do think that certain aspects of war may be futile. There have been attacks made in the past that have made no sense or have seemed pointless. It may also seem that the loss of human life in war is futile but this is inevitable.
I do not know that you can clearly say that war is futile. That's totally an opinion. For example, I would say that World War II was not futile in any way, at least not for the Allies. We had to fight and we really benefitted by fighting and winning.
You could argue that war is futile because even when we fight one war, there is always another war. So you might argue that war does not solve things. You can say that war must be futile because it does not truly resolve any of the issues.
This is more of a philosophical question rather than a practical one which can be answered based on clearly ascertainable facts.
I would agree that war is futile for the person who forces war on others because, what one can obtain from cooperation is much more than what is possible by force and war.
However war is not futile for one who fights to defend and protect himself or herself against an oppressor or an aggressor. In such cases, war may be the best alternative, irrespective of the ultimate outcome of the war.