Can your family force you to choose between your spouse and them?

I met my amazing gf last year and after a year of complete bliss, I've decided to introduce her to my family - I almost never bring girls home unless it's really serious. I met her parents and we got along great. However, when I introduced her to my parents, they acted like everything was fine and told me they didn't care that she is black and I am white. I recently told them I planned on proposing to her for her bday next month and my mom lost it. She told me she thought I was going through a phase where I wanted to experiment with dating a "hot black girl" and that she doesn't get why I'd want to have biracial kids. They told me I could find her equivalent in a white woman amd they would never accept her as my wife. I am outraged. My gf doesn't want to come between me and my family but I love her to death. I am ready to break ties with them unless they accept my future wife. I wish they'd understand but they are stuck in their mentality. What's the best way to deal with this situation?