That's a strangely narrow view to have. Any human organization bigger than a few isolated tribes in a remote location is formed by groups that differ from one another. If what you say is even minimally true, not a single nation can exist. After all, a "race" is just something you arbitrary define depending on the breadth of your experience with other groups. To the Ancient Greeks, the bordering Turks were a completely separate race. As people got to know each other better, the definition of a race expanded to include all Europeans (if we're talking about the so-called white race), justified through a vague sense of shared history. And nowadays, the idea of one human race is becoming more and more common, since we are becoming more familiar with one another.