User blog comment:B214/Volume 21 info & spoilers/@comment-27078744-20160725174830/@comment-114.4.78.82-20161001141133

@B they did actually try to cover that but if i am not mistaken Shiva said that they could not cover all the details about their existence, here is a quote from vol 21 remainin hopes

''“In the area that worships my mythology, through the rulers of the humans, we can fabricate or destroy records. However, there is a limit to that…there are simply too many details regarding this incident that we must not allow humans to know. Other mythologies are also in a similar situation. If the balance in the human world is tipped, the influence of mythologies will also be affected. This is something which must be avoided.”''

I guess vol 22 didnt cover in depth about this problem, but maybe the next volume or a sequel will.

Regarding the civil war problem, i agree with your point that Ajuka created the tournament to prevent that but if our speculation about the next villain is right (the 12 heinous criminals) then they could be the one who ignites civil war.