For around 500 years, war (and the deaths from them) were pretty consistently awful. Then as we entered the 20th century the military and civilian death rate soared as the world fought through two world wars. Since then, despite the headlines, deaths and wars have tailed off dramatically... until the last decade that is - which has seen the trend change significantly. With Soros among the many worried about World War 3, we suspect the current dip will be nothing but a positive outlier in history.
A recent paper, by Nassim Nicholas Taleb and Pasquale Cirillo, argued that our current peaceful era was a statistical myth: that dips in war deaths should be expected, as Roser's chart shows, and that there's no reason to believe this time should be different.
Pinker and others argue, by contrast, that things really have changed: that the rise of democracy, capitalism, industrial civilization, and international institutions like the UN have radically transformed the way global politics operates.
It's impossible to know who's right for sure. But Roser's chart makes clear that, whatever the reason, we should be counting our blessings today.