Why did they beat him up just because of our race?

hey, im 16 and iv just moved to south london from belfast in the north or ireland ireland. me and my brothers and my cousins have all moved together with our families and we go te same school. but the other day my brother got beaten up by some black kids apparently coz they dont want our types living round them. were perfectly capable of defending ourselves, i got about 15 cousins and 5 brothers, but IM not a fighter, alot of people where i come from do boxing and street fighting bare knuckle, but im kinda arty. my brother wants **** them up now, but i dont wanna get involved, this is why wee left belfast. what do you think i should do?