Class Alliance lore

Humans

Paladin: Human knights founded the original order of Paladins, the Silver Hand, during the Second War. Though the Hand suffered greatly during the Third War, Paladins still fight on in the defense of humanity.

Mage: During the war with the trolls, prior to the orc's arrival via the Dark Portal, high elven mages agreed to teach one hundred humans the arcane secrets of magic. After the war had been won, the humans and small number of high elves founded the Mageocracy of Dalaran. Dalaran fell soon after the start of the Third War, but by that time, mages had spread to human cities all over Azeroth.

Warlock: Since the destruction of Dalaran, there is no longer any major body of mages — like the Kirin Tor — to regulate the use of magic. Though frowned upon by society, many mages have turned to demonic magic in pursuit of knowledge, power or revenge against the Legion.

Priest: Humans have long followed the Holy Light, and it plays a major role in their society. Priests exist to guide their people in the ways of the Light.

Dwarves

Paladins and Priests: The dwarves were introduced to the Holy Light by humans and have adopted it as their religion. After the Third War, the humans began allowing dwarves into the Knights of the Silver Hand to repopulate the shattered order.

Hunters: The dwarves have long been renowned for their brilliant marksmanship and skill with guns. In recent times, the foundation of an Explorers' League has spread dwarven adventurers all across the globe.

Gnomes

Mage: With their intuitive and curious minds, the gnomes have great interest in all the sciences of Azeroth, and the arcane is no exception.

Warlock: In the same way as humans became warlocks, sometimes a gnome's pursuit of knowledge leads them down more dangerous paths of magical study.

Night elves

Druids: After the destruction of the Well of Eternity the night elves turned away from the use of the arcane and became wardens of the world they had almost destroyed. The druids were led by Cenarius's first night elf student, Malfurion Stormrage. The druid order was made only of males until the end of the 3rd War. The loss of druids during that war has led to some females entering the fold.

Hunter: Being defenders of nature, the elves are keen hunters. The closeness to nature which the night elves cultivate gives them a strong bond to animals, and elven archers have long defended Ashenvale from enemy invaders.

Priest: The night elves worship the Moon Goddess, Elune. The Priestesses of Elune have recently begun accepting males, just as the druids have with females.

Draenei

Priests and Paladins: Having been taught the ways of the Holy Light from the naaru, the draenei are a very religious race and priests are very important to them. They have long employed holy warriors in their fight against the Legion. Amongst the draenei, Priests and Paladins are known as Anchorites and Vindicators, respectively.

Shaman: The draenei were taught about shamanism by Nobundo, a Broken shaman.

Mage: The draenei/eredar are extremely intelligent and have a natural affinity for magic in all its myriad forms (according to the official Burning Crusade website).