How to combine worlds!!!!!

I need help! The story I am writing combines Peter Pan (Neverland and all that) and Alice In Wonderland. I need to combine the two, (Never and Wonderlands) but should I make them two different planets, or just two different countries? (Neverland eventually invades Wonderland) Thanks for your help!

For places as fantastical as Wonderland and Neverland, countries seem a tad mundane. the extra wonder and awe of two seperate planets, orbiting one another, is much more in keeping with the themes.

@Tarrant_Korrin Thank you!