The opinion piece outlines how the likelihood of a person's demise by violent means, namely war, has declined as wars have consolidated populations into communities and governments, growing ever larger over human history. In one way, war has made society safer and that safety has allowed society to focus on trade, which has made society and the individuals within society richer.
But the entire perspective of the article is focused on the winners of history. Those societies that won the wars have been made safer and richer. It can be argued that some of the conflicts in the 20th century benefited both winners and losers as wars over ideals and ideas supplanted those over religion, land, and gold, but that is only an argument. Over time, not everyone has equally benefited from wars - some populations became safer and others became more dangerous; some became richer and others became poorer.
If Morris' analysis differentiated how the losers of wars have fared in comparison, it may be stronger (or weaker), but it does not seem to. Morris takes humanity as a whole, but humanity as a whole is dominated by the conquerors - an us vs. them mentality that underlies Western worldviews.
It is important to not forget that these Eurocentric perspectives lurk behind much of what we consider as "normal." A great example is the world map - there is no particular reason for it being oriented the way it is:
(Source: Flourish.org, The Upside Down Map Page)