This is the background story for the Battle for Azeroth. After these events, king Anduin Wrynn as main leader of the Alliance attacks Undercity. In other words, at first Teldrassil and Darnassus get torched and burned by main leader of the Horde Sylvanas Windrunner which starts a great war between the Horde and the Alliance.
About 3.5 days since it came out to be exact. As I said, I completed everything there is to do in the Broken Isles. A special quest is activated automatically when you log in to the game if your hero has completed the 'The Battle for Lordaeron' campaign. Have you done every quest in every zone finishing side quest hubs in various zones will unlock more spawn points for world quests. It is worth noting that the prelude of new story is available for the characters at level 110 and requires the Battle for Azeroth expansion on board. The 'A Dying World' quest is a task which begins the story of this expansion - it should be completed if you want to unlock the necklace-artifact 'Hearth of Azeroth' and push the story further. Before the players set off to conquer new islands and zones, they have to go to Silithus and do special quest. It is no different in the case of Battle for Azeroth.
Every adventure has its beginning somewhere.
