Actually, most all peoples before the development of Christianity and Islam had a master race mentality.
I disagree. Christianity alone developed the very concept that of "all men are created equal," out of the Hebrew idea that all men are descended from one man created by God. The Jews never developed it explicitly because of their ethnic orientation. It wasn't until this Jewish idea was freed from an ethnic matrix that the idea of human equality could evolve.
Look at Greek, Roman, Chinese, Mongol and Japanese history if you don't think each group thought of itself as superior by nature to everybody else. The ruling classes in India developed the idea of caste as a way of perpetuating the master race. The Aztecs and Incas, in our hemisphere, had a very definite idea of their right and duty to conquer and rule everybody else.
In almost every language around the earth, the word by which its speakers refer to their own group translates as "The People," with the strong implication that other groups are NOT people. This implication is usually, although not perhaps always, made explicit by the terms used to refer to outsiders.
It is the idea of human equality that is unique and unusual, not the idea of human inequality. And of course if you believe humans are unequal, you will generally think of your own group as being at the top.