how has the doctor's "race" mistreated kinos "race" and why

From the text:

This doctor was of a race which for nearly four hundred years had beaten and starved and robbed and despised Kino's race, and frightened it too, so that the indigene came humbly to the door. And as always when he came near to one of this race, Kino felt weak and afraid and angry at the same time. Rage and terror went together. He could kill the doctor more easily than he could talk to him, for all of the doctor's race spoke to all of Kino's race as though they were simple animals.

The Spaniards have mistreated the Mexican people for years, taking their riches and using the natives for labor. This labor and misuse made the Spanish colonizers rich, and in turn, increased the wealth of Spain.