War is cyclical. There are many reasons why war is perpetual, including things like survival of the fittest and the will to power of all beings. Here are some more reasons why war brings more war:
There are certain groups who profit from war... politicians who gain domestic support and control, military corporations who make money from arms deals, and other corporations gain control over natural resources and/or expand their markets.
When someone who profits from war gains more power, they will have more ability, more influence, to ensure that war will continue.
The war machine is extremely costly to maintain. Billions of tax-payer's dollars are spend everyday. These are funds that could have been used for social services, like education, health care, and economic support for the disadvantaged.
A poorer, less education populace is ideal for maintaining war. War diverts funds from social services towards warfare, making populations less secure and less educated (and more likely to continue to fight).
Armies usually consist of young, strong men and women - young adults willing to fight and die for their country. War keeps them abroad, fighting other young, strong people, instead of staying home and fighting for democracy and equality in their own country.
In a way, war provides an outlet for the pent-up frustration of living in a war-mongering country, ensuring those who maintain the established injustices have less to fear from the new generation.
Tranquility of spirit and a calm state of mind come from relaxation and introspection. If we percieve an imminent threat (either real or fabricated), we will be less likely to be able to relax and achieve inner-peace. Living in a war-zone, or feeling like we are in a war, prevents us from finding peace within ourselves. If we cannot find peace within ourselves, we will be more likely to support war.
It is human nature to want to get back at those who have hurt us or the ones we love. While war may address our vendetta's against those who did us wrong, war is not the solution. War is indiscriminate killing... for every guilty party terminated, countless innocents, including children, are killed.
Revenge, being human nature, will also be a part of the humans on the receiving end of war. They too will want revenge. As there is no way to eliminate everyone (hopefully not, anyway), then war can only create new enemies, and ensure that war will continue indefinitely.
War is cyclical. If we do nothing, it will continue. It is up to anyone who wants peace to actively work towards achieving it.