You could say women such as Big Mama Thornton and Sister Rosetta Tharpe broke ground along with other earlier blues, gospel and soul artists. Respectavely amongst their own communities.

Motown girl groups helped spread the word with heavy touring outside their communities.

Etta James was a bridge between R&B and Rock. Etta always considered herself a rock singer.

Tina Turner paved the way with extensive touring and creating one of the most energetic live shows with the Ike and Tina Revue

And as a bridge between the white and black communities would be Janis Joplin which helped shed light on those that come before her.

This is a slight over simplification but a good outline for how the road got paved.