For the most part? I mean, there were these DS9 original things called the Prophets and the Dominion which I think played a preeeetty big role in the series.
Yes, but compared to the other two post-TNG Berman Trek shows, it focused more on building upon the foundations which were already established in TNG (and to a lesser extent TOS) rather than striking out on its own. Much of the starting premise of the series, from the Cardassian occupation of Bajor, to Sisko losing his wife in the battle of Wolf 359, to Dax being a Trill, to Quark being a Ferengi, to the uneasy peace with the Cardassians in the demilitarized zone, to O'Brien coming over, flowed out of what TNG had already established.