» Mon Dec 17, 2012 12:22 pm
It's all due to history.
The Orsimer, for the longest time, were considered on the same level as goblins and spriggans. Monsters to be culled. Orsinium, at that time well within High Rock, was basically the largest nest of the monsters. So, raids to Orsinium was basically an atempt to purge Tamriel of these warlik barbarians.
Then came the Dragon Break of 3E 417. Among the many changes, Orsinium became recognized as a member of the Empire, with all rights due to its people (the Orsimer) as are guarnteed to all citizens. This is a direct result of Lord Gortworg's petitions to Uriel Septium VII, and the reality-warping nature of a Dragon Break. Had Gortworg not been petitioning for recognition, Orcs likely would not have become part of the Empire.
And then the Septum dynasty ends on 3E 433, taking with it the 3rd era. Note that this means the orcs were only recognized officially for no more than 16 years. By the time of Skyrim, Orsimer has been a recognized nation for no more than 216 years. Considering that old nations such as Morrowind and Valenwood (which were officially recognized on some level long before the 2nd Era) had been taken over or ruined, it's not surprizing that the naturally warlike Orcs fought for expanding the borders of Orsinium, and having a pushback by more "civilized" races.