Greetings @rskills9002@gmail.com
When playing on our realms doing the storylines, then you would have to finish the zone that you started doing in the first place. This means that if you startes Zuldazar as horde then you would have to finish the storyline before you can start a new zone, in your case Drustvar.
Kindest Regards
Game Master Refrezh
Sethraliss - BFA