I will hesitate to wear these rosy glasses. The West has had somewhat peaceful 60 years, that's about it. See how liberal countries like Sweden suddenly close because of Syria? Revenge, hatred, and love are perennial notions, and they will always be part of the human psyche. The battle between good and evil has no ultimate victors or losers. Rationality does not explain what is at work here, it is not a deep enough human motivation.

If this sounds unconvincing, the Buddha and Christ preceded Hitler. Ashoka established a chain of veterinary hospitals in India in 360 BC, proclaiming that animals required equal treatment as humans do. [1] Are we "better" than these humanitarians?

Another example: India had no slavery in Greek times, and now has the largest number of slaves in history. [2] [3] I think similar cycles of rises and downfall can be seen in all the great civilizations, Egypt, Mesopotamia, China etc.

I don't know the answer, but history does not seem to be a linear progression from barbarism to civilization. It seems more like revisiting the same questions on good and evil, each time with more potent technology. The morality is the same, the technology progresses.

[1] https://en.wikipedia.org/wiki/Ashoka#As_administrator

[2] http://legacy.fordham.edu/halsall/ancient/arrian-bookVIII-In... paragraph X

[3] https://en.wikipedia.org/wiki/Slavery#Distribution