Can't Complete Achievement - Tides of Vengeance

The Tides of Vengeance achievement is granted for completing the Battle for Azeroth Alliance War campaign up through the 8.1 content. If you are having a hard time finding the quest you need next, check for orange exclamation points (!) on your Kul Tiras or Zandalar or in your faction's main city.

If you need further help, check Wowhead's Attunement Tracker to see which quests your character has completed.