"The only sound way to appraise the state of the world is to count. How many violent acts has the world seen compared with the number of opportunities? And is that number going up or down? [...] To be sure, adding up corpses and comparing the tallies across different times and places can seem callous, as if it minimized the tragedy of the victims in less violent decades and regions. But a quantitative mindset is in fact the morally enlightened one. It treats every human life as having equal value, rather than privileging the people who are closest to us or most photogenic. And it holds out the hope that we might identify the causes of violence and thereby implement the measures that are most likely to reduce it."