Originally posted by NewGuy01
Not really, the Sith have always been kinda around, even when they're gone. Vitiate's Empire, Rule of Two, One Sith, etc. etc. Also, the Jedi weren't really a thing until ~20,000 BBY, so I don't know what you mean by "tens of thousands of years" anyway.
The first Great Schism, the forming of the Legion of Lettow, the first darkside order, was in 24,500 BBY. They were wiped out completely.
The Hundred Year Darkness and start of Sith as we know them, as a force tradition, was in 7000 BBY.
There's 17,500 years where there were no opposing force orders, either in open or in secret.
Also, from the fall of Vitiate's Empire to the rise of Darth Ruin, was something on the order of 2,500 years, and during that time the only known Sith was the Lost Tribe, isolated on a single world.
While the Sith have been a major force in some parts of galactic history, the Jedi have gone much longer not being opposed by the Sith than they have with them.