In the Alabama of the 1930s, there resided in the state of the Deep South virtually only two races of people: blacks and Celtic or English whites. For, there was no industry that brought in immigrants from other parts of the world such as came to the North. So, any one who was Semitic or Mediterranean Caucasian, for instance, would be viewed by the residents of Maycomb as "dark" and foreign.
That the residents are fairly myopic in their viewpoints of others is evident in Scout's recounting of the Misses Tuitti and Frutti, whom she calls "Yankees" when they are simply residents of North Alabama and Republicans instead of Yellow Dog Democrats as so many Southerners were in the 1930s. [The antipathy for Republicans is a carry-over from the Civil War when Lincoln was president.]