An arguably even stronger influence, however, comes from the other side of the economic railroad tracks. Though few come out and say it, it is likely that many of the elite members of society approve of war not out of any sense of nobility or honor, but because war has direct extrinsic benefits for them. These benefits are both political and economic in nature, and tend to positively affect all of the elite -- those at the top of the economic, political, and military ladders. There is often, of course, a great overlap in these areas of power, which only makes the problem that much worse (Mooney & Knox 2007). It might at first be difficult to see how widespread death and destruction could benefit anyone, but it is actually quite simple.

The simplest and most sinister benefit is the economic one. War leads to huge increases in production and employment -- there are tanks, guns, and ammunition to be built, and this requires factories with groups of workers. There are also the soldiers that need to be clothed and fed, and all of the movements of troops and supplies requires some form of energy (usually derived from oil). All of these things require heavy amount of government spending, and the companies that receive these government contracts -- and the people that get the profits from these companies -- benefit hugely. The economy as a whole also tends to benefit from the increased...

This is more obvious militaristically -- war makes the military more important, and the more important the military as a whole is the more important its leaders will be, as well. A look at World War II makes this very clear -- the elite leaders of the military like Eisenhower and MacArthur at this time were some of the most powerful and recognizable figures of their era. Politically, too, the same basic benefit applies, as the elite leaders are associated in the public mind with protection of the country and its citizens. In addition, having a common enemy is one of the quickest and strongest ways to unify a people, and going to war against such an enemy is an enormous way to increase and solidify power in an increasingly centralized manner, meaning that there are even fewer members of the political elite wielding even more power (Mooney & Knox 2007).
Though these elites usually won't say that they really like war, history has shown individuals to be greedy and opportunistic. As long as there is profit, both in terms of money and power, to be had from war, there will be those unscrupulous enough to start it.

References

Mooney, L. & Knox, D. (2007). Understanding Social Problems. New York: Thompson/Wadsworth.