The Alliance is a union of major races of Azeroth. It was formed in order to stop the invasion of the Horde. Warcraft movie shows history of the Alliance from early beginning. Members of the union are: humans, night elves, dwarves, gnomes, draenei. This powerful union was founded by King Terenas Menethil II of Lordaeron and Lord Anduin Lothar of the kingdom of Stormwind after the First War.
You may also hear another name of this union - Alliance of Lordaeron. That’s because Lordaeron was the center of the union in the beginning. A lot of Humans moved to Lordaeron after the fall of Stormwind city.
After the First War begun, humans and other races of Azeroth fought against orcs independently. Such unorganized resistance was not very effective and the result of the First war was sad. Stormwind City, capital of humans, fell and humans had to move forces to kingdom of Lordaeron.
Terenas Menethil, King of Lordaeron, saw that orcs are serious thread and that it’s impossible to beat them alone. He called all seven human kingdoms to make a union. Arathor, Alterac, Azeroth, Dalaran, Gilneas, Kul Tiras and Lordaeron united their forces in order to confront the Horde. The Alliance was formed. Later on, Dwarves from Ironforge and Wildhammer clans, gnomes of Gnomeregan and high elves of Quel'Thalas also joined this union making it even more powerful.
Official Website: https://www.fightforthealliance.com/
Release Date: June 16, 2016