The Alliance
When the Legion arrived to Daaroth and Larium, each race tried to face the invader separately. However, this resistance was futile. There were too many monstrous beasts called mutants, and it was impossible to fight them on equal terms.
Only after reaching Tamrel Island, where apparently the source of evil was located, leaders of expeditions of the discordant races noticed that they would succeed solely by cooperation.
Commanders of the new-formed Alliance chose Harla Island as their base of operations. It was so tiny scrap of land that it was not even marked on many maps. The two islands were separated only by a narrow strait.
Thanks to the union of forces, the Alliance managed to liberate the town of Helmgaard and retake almost all Forest of Claws. Although the Alliance is in force only on Tamrel Island, it has already become a symbol of a fight with a common enemy.
Several months after the first victorious battle, the Alliance managed to establish beachheads in all areas of Tamrel. It would require much more time but for the ubiquitous Monesy who agreed to sell a map of the whole island to the Alliance, with marked locations of Tamrel portals.
It is year 1416. Almost two years passed since the first scouts landed on Tamrel. Now the war is raging, and worse still, nobody knows the real purpose of the Legion.
The Hierarchy
The Alliance has no commander-in-chief. Appointment of such a commander would mean an advantage for one of the races, and everybody wanted to avoid this. So the Alliance Council was formed, composed of expedition leaders of all races. Theoretically, the Council wields power over all forces of the Alliance. Practically, camp commanders in each region may take their decisions without asking for permission.
Simple soldiers form lower levels of the hierarchy. Base of the hierarchy consists of civilians helping with provisions.
It is hard to tell what is the position of scouts and spies. They are surely subordinated to the Council, but their relation to regional leaders depends on the situation.