As far as death tolls go the USA really didn't lose a great deal of people proportionately in the world wars. As far as casualty rates go the USA has done fairly well.

Still proportionately if 200K to 400K is going to stand out that much with the current population I would expect 300K give or take with a much lower population to stand out strongly.

Maybe they don't include war deaths in the data or something?

As far as death tolls go the USA really didn't lose a great deal of people proportionately in the world wars. As far as casualty rates go the USA has done fairly well.