Humans are i believe naturaly peacful and socially responsive,prefering to live in harmony with each other.The original condition of the human species is one of hunter gatherer,the skills required for hunting prey initiated a co-operative instinct within humans so as to maximize our hunting potential.People have lived within groups both large and small for most of human history.
With the historic development of civilizations however there developed new socio-political pressure,ie the appearance of religions,and new technological advances that ensured competition for scarce resources.Populations began to expand and complicated political frictions encouraged the militarization of societies.Although the above offers only a over simplified record of human history,the psychology of war developed as a response to the historical development of complex civilizations.
The advance of capitalism and the nation state further encouraged a centralization of political power,which in turn controlled the mass of population via strong propogandistic methods.This all remains a simplification of the facts surounding both the development of human civilzation and the psychology of war,however a picture soon emerges of the conflict and friction that these processes created.In the end analysis the answer to the question is humanity naturaly prone to warlike behaviour lies somewhere within what as already been discussed,however the complexity of the issues involved cannot be overestimated.My own personal inclination is that we all must be more tolerant of each other,alongside this i believe that real education must play a large part in ensuring understanding between all peoples and nations.The geopolitical situation as of this present time suggests that we have a long way to go as yet to achieve this goal,however it does remain possible.