Make a friend in another realm come into my alliance

Hi guys, I created an alliance that is working pretty well, after playing for 3/4 days I asked a friend to come and play with me but... we are in different realms, and can't reach each other in the game.

Will we be able to be in the same alliance some day ? It feels a bit stupid to me that we can't because it's the type of game I want to play with some friends. Am I missing something ?

Thanks for you answers.