That's a fascinating chart. Yes, it shows that war deaths have been decreasing for decades, but it contradicts that great-grandparent's claim that "life for the average human today is more peaceful than at any point in recorded history". Looking at the red line, it seems that there have been many peaks and valleys in the last 600 years. We're in a local valley (more peaceful period) right now, but it doesn't suggest a long-term trend to me.