Junon with its militaristic themes, soldiers and banners looks quite ww2 esque. But Rufus himself is more like Kim Jong Un to me: a ruthless young authoritarian inheriting an empire from his father.
Midgar could be a Japanese view of America: advanced, corporate, with unequal socio-economic divide, exploitative, domineering, had been in war with Japan (Wutai) and dealing with domestic terrorism. For a slum person, living on top of the plate would be an 'American Dream'. Additionally, remake's President Shinra looks laughably similar to Trump.
But reactors and ecological themes could have been inspired by the Chernobyl disaster, which caused worldwide panic in the 80s...
I think Sephiroth and Hojo are the most similar to nazis, Sephiroth is obviously like Hitler, considering that he sees regular humans as inferior to Cetra,
even though he's not a Cetra himself.
Hojo is like Mengele, an evil scientist that experiments on humans.