The author Desmond Morris discusses this question in his book “The Naked Ape”. He is an evolutionary psychologist who explains how natural aggression has become perverted in our modern society.
In the rest of the natural kingdom, aggression is used to maintain social structures, to maintain boundaries, and to protect oneself and family. In the animal kingdom, this seldom results in death.
Humans, on the other hand, have have had our natural aggression twisted into the pathology we are left with today. We have continued to separate ourselves from our oponents until we now can cause so many deaths by just pushing a sequence of buttons in a room on the other side of the world.
In conclusion, the answer to your question is no, war is not in our nature. But it is in our society, which influences our psychologies, our behaviour, our beings.