Short answers, pulled from the story.
The American Basketball Association was officially announced in February 1967 after a meeting of investors on the 20th of December 1966. Eleven teams were confirmed for the inaugural season by that time.
George Mikan served as the first commissioner of the American Basketball Association starting from its founding in 1967. He introduced innovations like the red-white-blue basketball and the three-point field goal rule to distinguish the league from the NBA.
The American Basketball Association merged with the National Basketball Association due to financial instability and protracted losses faced by most franchises. By the end of the 1975, 76 season only seven teams remained active out of the original eleven before four franchises joined the NBA.
The American Basketball Association introduced the first professional slam dunk contest during the final All-Star Game held in Denver on the 2nd of April 1976. Julius Erving won the competition with his free throw line dunk earning him $1,000 and a stereo system.
The American Basketball Association allowed Spencer Haywood to turn professional before completing his college career through a hardship exemption established in 1969. This legal precedent paved the way for other players to join the league early and ultimately led to the modern one-and-done rule in the NBA.