Is that why Battle Fever J structured their Rangers after Countries?
Basically, yeah. The lead character was going to be Captain Japan, the local counterpart of Captain America, until they decided to rework it into a Sentai series. This blog claims that Captain America was going to be a supporting character, but Universal had the TV rights to Cap at the time thanks to the Reb Brown TV movies, so they replaced him with Miss America.
It's also why the Battle Fever J helmets have sculpted noses and mouths to look like American superhero masks covering only the top half of the face -- which is why a lot of later Sentai helmets have sculpted mouths.