We can look at virtually any period of history, The Slave trade, Columbus' treatment of the Native Americans, torture in the middle ages, the holocaust, Mass raping and pillaging during invasions. I could go on.
There are still social injustices in the world, look at syria at the moment, Rwandan Genocide etc. Yet it is undeniable that we live in a less violent times and the majority of people would be appalled by certain things that used to be the norm. I.E. Slavery or persecution of a group of people.
How have we changed? Has a long standing history caused us to evolve? If so how?
Or has more regulation and global law preventing a true nature of the cruelty of humanity?
Steven Pinker in his book "The Better Angels of Our Nature" identifies five reasons:
The Leviathan - The rise of the modern nation-state and judiciary "with a monopoly on the legitimate use of force,” which “can defuse the [individual] temptation of exploitative attack, inhibit the impulse for revenge, and circumvent…self-serving biases.”
Commerce - The rise of “technological progress [allowing] the exchange of goods and services over longer distances and larger groups of trading partners,” so that “other people become more valuable alive than dead” and “are less likely to become targets of demonization and dehumanization”;
Feminization - Increasing respect for "the interests and values of women.”
Cosmopolitanism - the rise of forces such as literacy, mobility, and mass media, which“can prompt people to take the perspectives of people unlike themselves and to expand their circle of sympathy to embrace them”;
The Escalator of Reason - an “intensifying application of knowledge and rationality to human affairs,” which “can force people to recognize the futility of cycles of violence, to ramp down the privileging of their own interests over others’s, and to reframe violence as a problem to be solved rather than a contest to be won.