I'll start during the 1970's, around the time of the NBA-ABA merger.
1975-79- The Era of Parity: No dominant teams after the decline of the Frazier-Monroe Knicks, Wilt-West Lakers and Kareem-Oscar Bucks. NBA Champions averaged 49 wins during this era. Warriors, Blazers, Bullets and Sonics all won their only les during this era.
1980-1988- Lakers-Celtics Revival: Boston and Los Angeles went to the Finals every season, combined for eight les in eight years and went head-to-head for the le three times. Larry Bird and Magic Johnson were the dominant players in basketball during this era, although Michael Jordan began to make a big impact during the latter stages.
1989-1990- Bad Boys & New Western Powers: Detroit won back-to-back les in its mini-dynasty, while in the West Magic’s Lakers were supplanted by new teams that would make their mark in the following decade- Portland, Phoenix, San Antonio and Utah.
1991-1998- Running of the Bulls: Chicago’s six les-in-eight year dynasty. Yes, Houston also went back-to-back during this era. Sorry, Rocket Fan- your le teams will always lie in the shadow of the Bulls dynasty. You had great teams and their ’95 playoff run is maybe the most impressive ever- you can be satisfied with that.
1999-2007- West is the Best: Lakers and Spurs combined for seven les in nine years as the West completely dominated the East- with the notable exceptions of the Pistons in ’04 and Heat in ’06.
2008-2011- Superfriends: Boston’s 2008 le run inaugurated a new era as instant contenders vied for the crown.