Tiana is the first African American princess appearing as a main character in Walt Disney's Pictures. She's the 9th Disney princess following Snow White, Cinderella, Aurora, Ariel, Belle, Jasmine, Pocahontas, and Mulan. Rapunzel and Merinda came afterwards.
Although Tiana is a fictional character, she plays an important role amongst kids into Disney movies: They get to see that princesses come in various shades. Tiana is the first princess to enables little girls with a darker complexion to relate to one of the Disney characters in a positive light. As a kid I was never into the princess idea because I couldn't relate to any of the characters at the time. It's nice to know that at least now less kids will feel left out. Another positive impact from this is that it opens the door to a more diverse group of actors working at Disney World as princess impersonators. Let's hope, this is just the beginning of a more diverse cast of main characters from Disney and that future princesses will come in various shapes, size, colour and gender.