What forms of dance were the predecessors to breakdancing?

Break-dancing is improvisational. Break-dancers are influenced not only by dance moves, but also by gymnastics and the martial arts. 

The bouncing bass lines of funk and disco music allowed for a new fluidity in movement which entered popular dance in 1975. The Hustle, for example, incorporated movements of the arms, hips, and legs that were on beat with the music. Dance moves, such as The Hustle, followed the rhythm of music; whereas popular dances from...

Break-dancing is improvisational. Break-dancers are influenced not only by dance moves, but also by gymnastics and the martial arts. 

The bouncing bass lines of funk and disco music allowed for a new fluidity in movement which entered popular dance in 1975. The Hustle, for example, incorporated movements of the arms, hips, and legs that were on beat with the music. Dance moves, such as The Hustle, followed the rhythm of music; whereas popular dances from the 1960s, such as The Twist and The Hitchhike, followed the melody of a song and did not require much variation in movement.

James Brown is an important influence on break-dancing as well. As a funk artist, his style of dance was jaunty, but also incorporated spins and splits. He demonstrated gymnastic abilities on stage that would be featured in break-dancing. 

It is also possible that the lindy hop, a popular form of swing dance in the 1930s and 1940s, also influenced break-dancers. This style of dance, too, incorporated gymnastic moves, including high jumps, swinging one's body around one's partner, and sliding across the floor. 

Capoeira, a Brazilian martial art, incorporates dance. The performer demonstrates speed and flexibility. Back flips, somersaults, and cartwheels are featured. These moves also show up in break-dancing.

Break-dancing was about showing off one's physical abilities. Some New York street gangs had breaking competitions with their rivals. In these competitions, you could show a rival that you were not only a good dancer, but a good fighter. Breakers outperformed their rivals by being more innovative and complex in their movements. 

It is also important to remember that, though break-dancing originated in the South Bronx among black and Latino teenagers, it was and remains very democratic. Different people from different backgrounds began to participate and incorporated what they knew, whether it be a dances from previous generations, new moves picked up in a disco, martial arts, or gymnastics.