The article below is just a basic introduction to the topic. For something more advanced, written by pros and a fantastic leveling guide, my recommendation would be this Elder Scrolls Online Leveling Guide. I could not find any other guide that comes even close in terms of the impact it had on me.
The Aldmeri Dominion was formed by Queen Ayrenn to fight the forces and influence of Men. Supporting the Queen are Tamriel’s most loyal races: Altmer, Bosmer and Khajiit. All have united to serve under the Queen to win the war against Men.
Ayrenn views the humans, men, were unfit to rule Tamriel and its lands. Men were weak, fragile and before long, they die easy. Therefore, as justification, the ones that should rule over Tamriel as proposed by the Divines the 9 gods of Tamriel, was to be filled by the Aldmeri Dominion.
The Aldmeri Dominion controls the provinces of Summerset Isle, Valenwood and Elsweyr. The heart of the Dominion is located in Elden Root, concealed within thick foliage of Valenwood and guarded by the Bosmer.
This is one of the most strongly knit Alliances within Tamriel; their power, loyalty and purpose and a stubborn Queen maybe enough to claim a decisive victory Tamriel, towering over the other two Alliances: Daggerfall Covenant and Ebonheart Pact