You get 1+ in the stat that shows up in the leveling page, on every kingdom you get to L10. If you get 5 star kingdoms-very hard to get, it get 1 extra.
The bonus stats from levelling up a kingdom to lvl 10 are additive - I.e. all your troops will benefit (including your hero) from any and all the kingdoms you have at lvl 10.
Las estadísticas de bonificación de subir de un reino a lvl 10 son aditivos - es decir, todas sus tropas se beneficiarán (incluyendo su héroe) de cualquier y todos los reinos que tiene en lvl 10.
The more characters that you use from a particular kingdom the more bonuses that you will get, especially having unique characters.I often field this team…
Glade Warden/Legendary/21 Attack
Centaur Scout/Legendary/20 Attack
Skeleton
Star Gazer
But If you use 4 characters from ‘Forest of Thorns’ it boosts Glade Warden’s attack up to 22
I forgot to mention that getting a kingdom to level 10 will give you a + 1 boost of one of the following…armor/health/attack/magic. All of the characters that you use will get this bonus, even your Hero. For instance Zaejin gives one health at level 10, Adana gives one armor. To see what skill each kingdom will give just click on any kingdom, then on kingdom, on the ‘Kingdom Level’ screen you will see ‘Skill Bonus’. That is what skill that particular kingdom will boost. I hope this helps ya.