Prejudice towards the outsider was and is very common though, usually cloaked in ethnic or religious terms, and would feel in many ways similar to popular forms of 'racism' in our world. Sometimes it is aimed against fellow countrymen from a particular region or province that are considered somewhat 'Other' ('Welshmen suck, Bavarians are not to be trusted, Limburgers are clannish Papists and 'too Belgian' or 'too German'), in most cases a particular ethnicity / nationality is subject to strong prejudice.
Sure, I would argue the Albigensian Crusade was driven both by orthodox religious attitudes toward Catharism, and, to a lesser extent, the differences of culture between northern and southern France (the Languedoc/Provence).
The "Saracen" was the outsider/enemy because of their religion and homeland, not their olive skin.
You're right ethnocentrism is as old as the hills; the Chinese certainly thought Marco Polo was a barbarian, and promptly showed him how to make pasta.
That people like and trust people more similar to themselves; has certainly been true, for a long time. The idea that the human race (singular) can be broken up into sub races (like "Black," "White," and "Asiatic") and that they further can be differentiated beyond phenotype on the basis of other intellectual, moral, behavioral, or capable characteristics -- well, that's a new idea. Which dates to the 18th century.
As to what we see in Dragon Age, well, it seems to me the biggest forces of conflict are:
1) "racism" in the sense that the humans don't like the elves, and only get along with the dwarves because they need something they provide (lyrium) and are not interested in moving underground, so they don't want their territory.
2) clashes of religion (or ethos, since it's not clear the Qun is a religion per se), between Andrastianism and Qunarism ... with elvish and dwarven religion often being ignored by humans, though the humans do want to seem to bring the Chantry to them (see attempts to start Chantry chapter in Orzammar)
3) the different nationalities clearly don't get along; the one main national conflict we've seen is the distrust between Orlesians and Fereldans, it's why Loghain is doing what he's doing after all.
And oh, yes, of course, the mage-templar/chantry conflict. 