Britney Spears & Iggy Azalea

More than any other single artist, Britney Spears was the driving force behind the return of teen pop in the late '90s. The blockbuster success of the Spice Girls and Backstreet Boys certainly paved the way for her own commercial breakthrough, but Spears didn't just become a star -- she was a bona fide pop phenomenon. Not only did she sell millions of records, she was a media fixture regardless of what she was (or wasn't) doing; among female singers of the era (many of whom followed in her footsteps), her celebrity star power was rivaled only by Jennifer Lopez. From the outset...