Conventional history has long shown that, in many ways, we have been getting kinder and gentler. Cruelty as entertainment, human sacrifice to indulge superstition, slavery as a labor-saving device, conquest as the mission statement of government, genocide as a means of acquiring real estate, torture and mutilation as routine punishment, the death penalty for misdemeanors and differences of opinion, assassination as the mechanism of political succession, rape as the spoils of war, pogroms as outlets for frustration, homicide as the major form of conflict resolution—all were unexceptionable features of life for most of human history. But, today, they are rare to nonexistent in the West, far less common elsewhere than they used to be, concealed when they do occur, and widely condemned when they are brought to light.I suggest reading it in full.
The basic yardstick that we can use to evaluate such claims is to compare our generation with the generations before. Do you think that we are on the whole more peaceful than our ancestors? Barring a few notable exceptions, the answer is a resounding "Yes" almost everywhere in the world. Is there a convincing reason that this trend which has been going on for centuries is going to overturn? With nuclear weapons and more powerful technology to produce weapons of mass destruction, probably there is. But the more powerful and faster moving trend of globalization partially negates that threat too.
Somewhat similar to "The law of accelerating returns" for progress, the law of decreasing violence probably follows the inverse exponential trend. Continuously decreasing but never quite reaching zero.