Last year I heard a lecture by an American social scientist who said that until fairly recently (1950’s) many states in the USA still had laws forbidding interracial marriage. That of course gave rise to the question: who belongs to what race. As he explained it, there was considerable discussion (were Asians a different race? Were people from Latin America ‘black’ or ‘white’? Could Latin Americans marry Asians?), and different states had different categorizations. The start of these laws according to him was the pre-Civil war era. Many slaveowners had illegitimate children with their slaves, and if these could be recognized (for example by marriage) the white families would have to stand substantial losses in property as a result of the children having a right to part of the inheritance.
I’m afraid since this was a public lecture that I don’t have a cite handy. It does however give an explanation as to why the concept of a ‘hispanic’ race still lingers on.