The Fallen of World War II
I'd go so far as to say this is a must watch. It's a fantastic visualisation of the death counts of World War II and how they compare to other wars.
Some of the moments in that video are eye-opening in a way I didn't appreciate before. In particular, the staggering number of Soviet casualties is jaw dropping when put into scale.
I guess the only slightly disappointing part of the video is it kind of felt like the author chose to spend too much time on Europe and kind of glossed over the Asia part. Maybe there will be more videos.