The Changing of the Guard
What one or two year periods seem to be a transitional period (changing of the guard) in tennis history. I'll use '78-'79 for an example. The names of Wade, Reid, Casals and Durr had been fixtures at the top of women's tennis. Stove had risen to prominence after a long career. New faces, Austin, Shriver, Mandlikova, Jaeger and many others who would impact the top of the rankings made their initial run during this time.
What other periods of great change do you see?