Horde Suramar 110 - step 386

[jerioke]

You can not accept Building an Army if you have not turned in Uniting the Isles and unlocked "World Quests".

This has been noted in the Withered Training Section of Wowhead's Suramar guide.

[ZG Support 1]

You need to unlock the World Quests for the World Quest version of the Withered Army Training. This quest is for going thru it the first time when it's not yet a World Quest and does not require having World Quests unlocked yet.