Since the advent of liberal democracy, the degree of violent death has decreased exponentially. Yes, when major conflicts occur, they are far more devastating. However, if the same proportionate amount of people died at the hands of their fellow humans in the 20th century as in the pre-modern period, there would have been two billion deaths from warfare. Not 100 million. You can literally see that deaths from violence are decreasing by the decade, world-wide.
Since the advent of liberal democracy (and communism: they have the same effects) population has also exponentially increased. Which is worse, violent death, or mass early death due to over-consumption of resources? The level of violent death in earlier ages helped off-set the unnaturally destructive increase in population we are experiencing now.
Also, the type of violence was not wholly unhealthy as is it is in modern warfare; in fact, it was extremely biologically beneficial. The healthiest, strongest, most intelligent, most fit specimens survived to the greatest degree: it was positively selective. Modern warfare is impersonal, relying on technology rather than individual prowess and strategical genius. It kills without discrimination: fit and unfit alike.
But, anyway, this has nothing to do with the systems of gov't or societal organization. The numbers have to do with primarily technology. Modern advancements allow for quicker wars with less overall casualties. Whilst ancient methods of warfare were much more to-the-last-man, as one man
could hold out against many. It doesn't matter if people live in tribes, nations, or a global society: swords require much more unmitigated methods of battle than bombs and guns. Communication and transportation advances also greatly expedite conflicts. It has little, to nothing at all, to do with the basic form of social organization & government.
Not to mention the massive cheapening of life liberal democracy has brought.
I don't think that you can say that war is a natural inevitability either, it's too recent a practice to have been shaped by natural selection. If it is inevitable it is because of tribalism and nationalism, that is select ingroups fighting over scarce resources.
Too recent a practice? Warfare has been practiced since recorded human history. What has tribalism and nationalism have to do with it? Nationalism is national pride & identity, and the belief in its preservation: nothing negative to or intrusive upon other societies. It hasn't a thing to do with thinking your nation or ethnic group has any more of a right to exist than any other. That ideology has simply existed parallel with, but still not tied to, nationalism, to a historical extent so great that we've wrongly associated the two: it stems out of nationalism, but goes far beyond it, making assertions which require a nationalistic base but are not in themselves nationalistic. And, again, what logical tie does tribalism have with war? They are separate entities entirely, associated as they are due to another massive misconception: just because they've existed together to a great extent we tie the two together without any reason aside from that. It's like saying long hair defines someone as being female.
Warfare stems from mammalian and human nature, not nationalism, not tribalism. Mammalian nature is to compete, with violence, over resources (habitat and food) and mates. Human nature to organize into social large social units (tribes, states, nations, etc.), which develop an identity and work together for survival. In a way, these units become living organisms in their own right, with specialized parts working together for the health of the whole. And as is mammalian nature, these units compete, with violence, over resources; which on the large scale, as it occurs naturally with the human species, is called war.
