https://www.polygon.com/2018/8/2/17617618/world-of-warcraft-battle-for-azeroth-alliance-zone-preview-impressions

World of Warcraft: Battle for Azeroth is doing something Blizzard’s MMO has never done before. Instead of both factions leveling in mostly the same set of zones, the Horde and Alliance will each have their own continents all to themselves. The opposing faction players will eventually establish a foothold on the other continent, but during leveling, Alliance players will rarely run into the Horde. World of Warcraft: Battle for Azeroth is doing something Blizzard’s MMO has never done before. Instead of both factions leveling in mostly the same set of zones, the Horde and Alliance will each have their own continents all to themselves. The opposing faction players will eventually establish a foothold on the other continent, but during leveling, Alliance players will rarely run into the Horde.

This new change leaves each faction with their own “home” zones. Each continent — Kul Tiras for the Alliance and Zandalar for the Horde — has three zones for their faction players to level through.