This is a variation on the Olympic Medals Timeline visualization, showing the countries winning Olympic medal in long-distance running (marathon, 10k or 5km, men or women). You can see the dominance of the Flying Finns in 1920s and 1930s. Starting with 1960s, independent African countries start competing in Olympic games and Ethiopian and Kenyan athletes become dominant winners in 1980s and even more so in 1990s.
Are you interested in other sports instead? This visualization is configured to let you easily
pick other sports in athletics. Just click on "options" and pick short-distance running sports
instead! If you want to experiment more, you can change
'by sports'.Athletics in the source
code to another category and then choose whatever sports you want to see. For example,