When was the last time a player ended two years ranked #1 in the world for back to back seasons before the Nadal and Federer dominance?
Hewitt, 2001 and 2002. I would not include Nadal in the "dominance." Definately on clay, more than any other player in history on a surface. But, Nadal has only 2 years number one, non-consecutive, compared to Federer's 5. And only about a third of Federer's weeks at number one.