There is a Breaking News up that says the following:
Realm Connections - August 20th, 7:00 AM - 3:00 PM (PDT)
The following realms will undergo maintenance to complete their connections:
Eldre’Thalas, Korialstrasz, Akama, Dragonmaw, Mug’thol, Korgath, Cenarius, Perenolde, Cairne, Blood Furnace, Mannoroth, Nazjatar, Azgalor, Azshara, Destromath, Ursin, Andorhal, Scilla, Zuluhed, Eonar, Velen, Madoran, Dawnbringer, Azuremyst, Staghelm, Garona, Icecrown, Malygos.
It’s been up for several days but you may not have seen it before maintenance began.
For more information check out the post in the General discussion forum.