Great question. My guess is that in our early stages as small tribes of hunter gathers, we were pretty compassionate with regards to other members of our own tribe because we knew we relied on the group for our very survival. But we were utterly heartless with members of other groups. Tribal warfare was commonplace and deadly. The vanquished were either slaughtered immediately or enslaved and worked to death.
As population density grew, what had been the tribe expanded to the city state, and eventually grew to include national borders with numerous cities inside them. But the warring went on unabated. We had a very long Age of Conquest where the way to glory was through rape and pillage expansion and leaders like Alexander and Genghis Kahn got “The Great” tacked onto their names by being the most rapacious, murderous human of their time.
The Age of Colonization changed the equation a bit. When the base of power shifted from the East to Western Europe, the European nations intent on dominating one another sought to do so by taking over nations here and there around the world, and sending out explorers to claim new-found lands in the Caribbean, the Americas, Australia, and New Zealand; even if those “newly discovered” lands already had people living in them. But to profit from those lands over the long haul, they recognized that they could not just cart off the gold and silver they found there; they needed human capital for agriculture, crafts, mining, logging, and trade. And so things got a bit less violent than they had been back in the Age of Conquest.
As we approached modern times, outright colonization gave way to neocolonialism, where global capitalism and imperialism replaced outright conquest. The powerful sought to dominate weaker nations through economic means, but still to dominate them. This led to some spectacular wars like WWI and WWII, with destruction on a scale the world had not seen since the Great Kahn was sweeping across the know Earth destroying all who refused to bend to his will. But WWII ended with a game changer. The nuclear age dawned with the destruction of Hiroshima and Nagasaki.
As the former allies in the Communist block countries and Capitalist West split apart and became instead of allies mortal enemies, each pushed their own nuclear weapons development. The result was that hydrogen bombs with 3,000 times the explosive force of the bomb that destroyed Hiroshima were soon in each nation’s arsenal. The world soon recognized that WWIII, fought with the nuclear capacity to destroy all humanity many times over, was unthinkable. The age of MAD (Mutually Assured Destruction) dawned, where the only way to shoot your opponent was to put the gun to your own head and blow your own brains out in the process.
MAD had given the first glimmer of hope that mankind might learn to limit warfare. We have actually restrained ourselves from launching another all out war for some 77 years. That’s unprecedented. We have also begun compassionate outreaches to areas devastated by famine, drought, AIDS, and natural disasters. Compassion has been on the rise. The greatest threat I see to that trend continuing is the rise in power and appeal of apocalyptic, fundamentalist religions that actually yearn for the destruction of all mankind so that a handful of “true believers” can meet up with their imaginary friend in their imaginary Valhalla in the sky. Stay tuned. It remains to be seen whether reason or irrationality will prevail. And that, my dear @tups, will ultimately answer your question.