The four nations,what does it mean?

Every one knows that The Avatar is just a story but there actually is some truth behind it.First thing You see those chinese characters a the top of the picture,well they are real characters.It says"The heroes divide the world ",then it says in the corners the elements which are (water,peaceful) (earth,strong) (fire,fierce) and finally(air,harmony).Then at the bottom it reads:"correct things under heaven".Not just the characters are real but the bending moves are real too.There based on real moves and styles,like aang uses a style called Bagua which is circular moves defense and offense.Toph uses a style called Southern Praying Mantis which uses strong footwork and very special movements.Katara uses moves called tai chi which makes the chi flow in your body to make effective defensive moves.Last but not least firebending which is based on Northern shaolin style and uses almost all offensive moves like strong kicks and fast moves.That just shows you anything can have a meaning