Can't Complete Quest - Warchief's Command: Desolace!

If you are not able to turn in the breadcrumb quest Warchief's Command: Desolace!, it means that you have completed one of the follow-up quests in Desolace, which will prevent you from turning this quest. To fix the issue, simply abandon the quest, as it does not affect your progress in Desolace. 

Note: You can find the full quest chain under Series on the Wowhead page linked above. It is possible to start the questline with the quest Avenge Furien! in Desolace.