BFA faction assault unlock

I’m levelling some alts in BFA. i’ve done faction assaults before.

What do I need to unlock Faction Assualts on each new character (get the quest to talk to Nathanos Blightcaller)?

A certain level?
A certain number of BFA War Resources?
Both?

I think for alts, you just need world quests unlocked. I don’t remember encountering any walls.

What is that? I’ve done the intro to go Zuldazar. I have some world quests. They aren’t locked.

On some alts I was in my 30s before I got the first faction assault quest. I currently have an alt at 31 and another at 25. They don’t have faction assaults.