I am completely stuck on the Ready For War achievement. I’m trying to unlock the Mag’Har orcs and do the Pathfinder achievement but Nathanos is not offering the next quest. I have completed the Zandalar story line, got my Heart Of Azeroth, done three of the previous steps of Ready For War but now nothing. All the info online says to get your Heart of Azeroth but I already have that and the only quest in the Chamber of Heart is Wrathions “Visions” quests.
Did you unlock BFA world quests?
Yep, world quests are unlocked.
I would suggest you check out this guide on the issue as it appears you have already completed the quest you are looking for and are further through the chain.