In U.S., going back to 19th Century pre-modern Olympics through modern Olympic era, historically, U.S. is the best 400m nation in the world. Must be more cultural than genetic since it was mainly White U.S. men dominating 400m dash in earlier years. If 200m dash, 110mH and 400mH are added, U.S. historically is the best long sprint nation in the world.
As we know, Kenyan men earned Olympic medals, 1968 & 1972, 4 x 400m relay. Since then, it seems Kenyan men capable of sub-45 400m are okay with 45.xx or 46.xx 400m and are choosing 800m as their primary event.
Kenya is due for solid 200m & 400m specialists. Bell curve. As we see some talent from 400m in U.S. spill over to occasional 800m talent, we should see some of Kenya's 400m talent show in occasional 200m talent, even 100m every now and then.