User blog comment:Avery D. North/Great Kingdom/@comment-244290-20160307073403/@comment-181.230.122.206-20160307082933

It makes no sense. If the Kingdom was there, how were they destroyed? I mean, the island can't be found...

I believe that the Kingdom was betrayed by some of their people. In the Image that appears when Clover is explaining about this Kingdom, the buildings and structures have a similar appearance as the Structures on Mariejois... (The windows for example)

There's always some people that doesn't agree. I mean, opposition. So, they deserted from the Kingdom, talked with some Kings, formed the Alliance, and as the final act of betrayal, they lead a great army to Raftel and won the War.

That would explain the similarity in structures and the reason why they knew so much about them to the point of finding their secret island.