There is a theory in my mind, and knowing the way how Kishimoto thinks it may be a possibility too. Since it is a fact that Naruto itself includes different historical or biblical/religious elements. For example Kaguya , judgement day.
Firstly, we know that Kaguya wanted to erase the shinobis and recreate the world to start another era. There are different theories about such things. I don't think if I have to present any of them. We all know that Kaguya failed, but the fact is she wanted to restart and keep this "cycle" up. During that battle against Kaguya it turned out that those white Zetsus were people from the previous era.
Secondly, if we think this way, we also have to consider another thing. The planet where shinobis live is also called Earth (as it was mentioned in the previous naruto movie too). Maybe landscapes and continents look differently, but we all know they are moving due tectonics.
Finally, we came to my theory. What if Naruto is taking place in a post-apocalyptic world? After "our" world. So the battle against Kaguya was about to stop this cycle. We got familiarized with Kaguya's story too. That included the turn of people into shinobi, but if the people from previous era became white zetsus, then they couldn't be equal with the "first" Shinobis. That is why I think Naruto's world is taking place in a post-apocalyptic world.
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