User blog comment:Joekido/The loopy side of the Void Century/@comment-4623405-20200917203313

Here is my theory:

The great kingdom of the void century is not as unkown as we think. It has actually been mentioned in the series. But that was before Robin's flashback. The great kingdom is actually Shandora, being mentioned in the Sky Island saga.

It is a known fact that Shandora was destroyed during the void century in war against the 20 kingdoms. That information is even on this wikia.

Why 100 years exactly? Well Shandora was a well hidden kingdom, it's a possibility that the world just didn't know about it at first. It's possible that they raised their power during that time and became a threat to the other kingdoms. After all, the Shandia are a tribe of ruthless warriors. But in the eyes of the other kingdoms, the Shandia were beneath them. "How dare those wild creatures put up a fight like that against us civilized people?". In the war the 20 kingdoms suffered great losses. So they removed the war against Shandora from the history books because they didn't want to admit almost loosing to a bunch of "wild people".

After all, when Mont Blanc arrived like 400 years later the kingdom was totally unknown to anyone, and the Shandia didn't know anything about the outside world. And because they were shot up Sky Island and stayed there for another 400 years, the history was never revealed. After all, Sky Island is a myth to most common people itself.

And even if someone from the blue sea found their way up with the knowledge of the void century existing, they wouldn't make the connection.

These are my thoughts at least. I mean, it is a known fact that Shandora was destroyed during the void century. And what are the odds of a second great kingdom that existed and was destroyed in a similar battle during the same period?