I am still wondering how Blizzard make the Siege of Orgrimmar doable for Alliance.
Why? Alliance have tried numerous times to invade Durotar. Orc/Troll players found many invasions plans last couple of years in Durotar. Alliance haven't set foot on Durotar succesfully once. Every camp they try to build is burned down by the Orcs. Apparently Barrens is filled with Korkron guards as well in patch 5.3. So Orgrimmar is protected on multiple sides.
So how are the Alliance sieging Orgrimmar?