Tamriel wasn't doing so well after the arcane explosion four years before that caused mages went insane and die. The Daedra began multiplying one after another, creating a sort of hell for the world. Molag Bal, who was the Dardric Prince of enslavement and domination, wanted to weaken the barrier between Nirn and Oblivion so he could press it together to form a single world of pain and suffering.
Regardless of the hell that continued to boil, three alliances were formed: Daggerfall Covenant, Ebonheart Pact, and Aldmeri Dominion, which were made up of certain races that came from similar areas of Tamriel. Each alliance, while fighting for their own personal reasons, are also fighting the dark forces that Molag Bal unleashed upon them. These are TESO Wars.
The High Elves were the first race to set foot on the soils of Tamriel, therefore they believe they are or should be considered the rulers of Tamriel solely based on their history. Of course, when their Altmer queen starts to play a role by telling her Dominion that she "doesn't hate the other races," but doesn't believe they should rule, because they "don't have the wisdom that comes with age," she gains many followers. She is after the Throne of Tamriel, and of course the High Elves stand by her as do the Wood Elves and the Khajiit.
High King Emeric of the Daggerfall Covenant tells his followers that the people are suffering, starving, and not getting what they need due to the "pretender" that sits on the throne and rules Tamriel. Emeric is a Breton who gained his alliance with the Redguards through marriage and gained the alliance he has with the Orcs by presenting them with a war treaty, which also allowed them their homeland which was restored, therefore they owe a great debt to Emeric.
The Nordic Jorunn is the leader of the Ebonheart Pact, which is formed of Nords, Dark Elves, and Argonians. The history between all three races is displeasing, however, Jorunn created a governance system that has helped them see past the discrimination and slavery history they all have. This type of governing, called The Great Moot, involves Jorunn having his decisions approved by the Nords, Dark Elves, and Argonians before they are set in stone.
The Elder Scrolls Online history is like a more-confusing-than-usual puzzle that adds a piece just when you solve another. Something is constantly being added and found out. There is bad blood between some races while others are much closer. Some races put their hatred for each other aside to be civil for the sake of helping someone they want as their king. Each alliance has a lot to deal with between the alliance war they're having with each other and fighting off Malog Bal's dark forces while also stopping him. These alliances have a lot on their plates.