I actually posted this in another forum but never got replies >_<.
I was discussing this for another one of my friends from IRC ^^, since we are writing a fanfiction bridge for the ending of the SK manga and the Funbari No Uta. (We both actually work quite closely with the manga so ya-- we researched this a lot)
I was discussing with him about the Island of Mu and whether it was a possibility that it was the lost city of Atlantis, since it was obviously a big deal and under water. Instead, we found it was a real mythological island (more info can be found
here) and then thought of a reason why Mu was important. All in All this our theory we came up with, and since my fanfiction is a bridge I was trying to connect the history of Mu to Hao's deeper desires of destroying the human race (of course I will probably go into more detail on it later) but this is basically what we thought up, and I thought I might share it with you all XD.
The people of mu, were shamans using and protecting the Elemental Spirits, but they eventually overused the spirits, and caused the Ice Age (yes the first ice age of man-- you know how Takei likes to throw in weird theories, so I thought I might too XD) . Thus, to survive, they perserve and live in plants (this is WHY there are so many plants and of differen types etc and their technology is great.). to perserve life, but when Ice age is over, the Shaman King, with his Great Spirit banishes them into the deep for punishment (why the humans never got hold of that technology). I actually have a whole more lined about about that, but;
related to Hao,, he knows a lot about the history of Shamans, and probably knew all this, and if not, has taken notice of the human race destroying everything (even Horo says this remember), after all he knew about Mu: and an additional reason he might want to make a new world etc. is sort of like not REVENGE, because Hao isn't that petty quite seriously, but also because the humans are exhausting the sources of the earth quite quickly, and he wants to kill them off and create a strong world of Shamans for this reason. The Nature theme is something I find interesting in SK, and I thought I might discuss it here XD but ya, that is my plan, but I thought I might throw it at you all. But ya, my random thoughts.