Three videos taking a look at how Japan evolved during the medieval period.
The first video, by Hurricane Hunter03, shows the history of Japan from 4000 BCE to 2018 CE, and offers a good look at the internal border changes when Japan was split into various competing states.
Mapping History has also created a good video, starting in 1185 and going to present
Finally, for a broader look at the region, take a look at EmperorTigerstar‘s video showing East Asia
You can also watch this video on The Japanese Animated History In a Nutshell from Knowledgia