We fight so much because it is natural. In nature, animals fight to defend their territories, their nests and their homes – it is natural; and we are animals, or rather, we have taken on the physical and mental characteristics of an animal – hu-man, and are in the process of jettisoning these characteristics.
However, we are Spirit, and it is spiritual not to fight or defend anything*. Behaving spiritually, if another comes to take our home or territory, we would gladly hand it over and there would be no fight. There would also be karma accruing to one party only.
So, we fight because our animal instincts are still stronger than our inherent spiritual qualities.
*We defend things because of attachment to the things, and attachment is not of the Spirit.