I compare it to boxing matches. If I'm watching a match between someone who is identified as German, and someone who is identified as Italian, without other influences, I am going to tend towards cheering for the Italian, because I identify more with Italians. Never mind the fact that I'm 3/4th German and only 1/4th Italian, and certainly don't have anything against Germans. It's purely a unconscious tribal reflex, rarely even noticed unless given a chance to magnify (time and numbers provides this magnifying factor in communities.)