Board Thread:Theories and Speculation/@comment-28819877-20170801141801/@comment-28819877-20170802071437

Perhaps i mistakenly called world as shinobi world. Ordinary people also live there. So i presume they become scientists/historians because both they and shinobi obviously share our nature - desire to know everything. So appeare of supernatural things like chakra and Ten-Tails can be considered as revolution of people's understanding of universe and creation of manuscripts.

So either all of them were really destroyed by BZ as stated above or permanently damaged by previous world wars(unlikely).