The Alliance has historically been the main alliance of human kingdoms & their allies.
Alliance of Lordaeron: The Alliance of Lordaeron was formed to stop the Orcish Horde’s invasion of Azeroth during the Second War (year 4). It included the high elves of Quel’Thalas (now known as blood elves).
Alliance (playable faction), AKA Grand Alliance: After the fall of Lordaeron against the Scourge (year 20), a new Alliance was formed, and is one of the two playable factions in WoW. It includes the humans of Stormwind, dwarves of Ironforge, gnomes, night elves, draenei, worgen and a number of allied races.