Human beings are inclined towards both peace and war. Even political and social causes of war can be regarded as ‘natural’.

• It could be argued that war is not natural on a biological level as recent research suggests that early Hunter-gatherer societies rarely engaged in it. Studies say that most violent deaths among these societies were revenge killings, individuals killing others, or family feuds, and only a tiny percentage can be attributed to war.

• However, I would argue that war is still ‘natural’ as it did still exist in these times. Furthermore, the causes of war which are based on social/political factors are still ‘natural’. Liberals attribute war to political structures whereas socialists attribute it to class structures. Autocratic governments and capitalist societies can be seen as a natural result of ‘natural’ human interests: desire for wealth and power.

• People are also ‘naturally’ inclined towards peace, which international agreements show. In times of war, most people desire peace because of the suffering that war brings. However, I think there will always be people who would prefer to put a country in a state of conflict, making it ‘natural.’

It's possible that war is not humanity's natural state.

• R. Brian Ferguson from Rutgers University argues that collective killing as an output of cultural circumstances may only have emerged recently in human history---within the last 12,000 years.

• People may kill on a personal level because of innate, violent tendencies, but the action on a collective scale, the argument goes, is likely related to cultural conditions rather than any inborn traits of our species.

• "The preconditions that make war more likely include a shift to a more sedentary existence, a growing regional population, a concentration of valuable resources such as livestock, increasing social complexity and hierarchy, trade in high-value goods, and the establishment of group boundaries and collective identities," Ferguson writes.

• As Laura well points out, if we want to include societal and cultural conditions within the realm of anything natural about our species, then war may still be our natural state. Some may wish to do this, arguing that culture and society are also part of our natural makeup, perhaps even in the same way genes are. Including cultural conditions would just demand we call on a more extensive form of causation, a form that exists beyond our bodies in a way that is no less related to "us" than other aspects of ourselves we think about.

• Overall, I think war could be considered unnatural, though, if we think about how hard it is to consider something natural, anyway. I say this perhaps only because I'm swayed by Ferguson's argument in spite of finding it difficult to pin down factors, both internal and external, related to "naturalness" in the course of human existence.

Humans always lean to violence to solve problems.

• Too often violence and war seems like the easy way out of a problem. Annoyed with your mate? Punch them. Annoyed with a country? Drop a bomb. This seems to be humanities solution to any problem.
• A quick and easy solve, with consequences considered later. we have been solving problems like this since we began, from ancient dynasties and to modern wars. We rely on violence to solve our problems.
• As long as we are human, war will be our affair.