At the beginning of the 1979-1980 season, the National Basketball Association made a rule change, adding a three point field goal to the game. The three point shot had been used in the recently-dissolved American Basketball Association, for the reason that it opened up the court and led to more unexpected game play. While some fans thought it was a gimmick, and it took a while for teams to use the shot as a regular part of their offense. However, the three point shot gradually changed the game of basketball.
But at the time, the addition of the three point shot probably didn't seem like the most significant thing that happened that year. In 1979, Magic Johnson joined the Los Angeles Lakers and Larry Bird joined the Boston Celtics. These two were already recognized as great players in college, and them playing for two of the NBA's greatest teams quickly brought more publicity and excitement to the league. They would be the first superstars in the league, but many others would follow, especially Michael Jordan. Basketball, which had been the third most popular American sport throughout the 1970s, quickly became the most popular, with its dynamic and personal play complimented by the "coolness" that came from the association of basketball with black urban culture.
The game changed at the beginning of the 1980s, both on the court and in people's perception of it. The changes in the game that happened after the introduction of the three point shot were not directly caused by that rule change in the way that introduction of the shot clock changed the game, instead being the result of several things: the absorption of the American Basketball Association into the game, the entrance into the NBA of some of the greatest players ever, and the changing demographics of the American sports audience.
But the introduction of the three point shot seems to be the easiest way to denote the change in how basketball was played. Although creating "eras" can sometimes be a game of artificial history, it seems like a fair way to divide what came before from what came after. And much as what I wrote about the Shot Clock Era, the introduction of the three point rule seems to be a good way to avoid unfair comparisons. Was Shaquille O'Neal, who begin play in 1992, a better player than Wilt Chamberlain, who begin play in 1959? Was Michael Jordan, who begin play in 1984, a better player than Oscar Robertson, who begin in 1960? These comparisons are somewhat unfair, because the game changed its character so much beginning in 1979. While the exact impact of the introduction of the three point line, and other changes in play can be debated, most basketball fans would probably agree that the concept of the "Three Point Era" makes sense.