LogFAQs > #967646624

The Federation/Cardassian war is brought up in season 4 of TNG, and it's revealed that O'Brien fought in it before joining the Enterprise crew, and still has a dislike for Cardassians as a result, but you don't actually see it, it's more like they created the Cardassians as a new baddie, and rather than spending time giving them an origin/first contact story, they basically just said that there was already a history there and cracked on with it.

Given the timings mentioned in their first appearance (the war has been over for less than a year, IIRC, and the peace treaty is still being worked out) this means that the Federation were at war during the opening season of TNG and not only did the fleet's flagship not take part at all, it never even once got brought up in conversation.

To be honest, as long as you know who O'Brien and Worf are, then for the most part the only TNG lore you need is the Battle of Wolf 359 to get Sisko's situation in the pilot.

There are guest appearances from Q, Vash, Tom Riker and the Duras Sisters, and Gowron has a pretty significant recurring role, but while you would definitely benefit from having seen their TNG episodes, you get pretty much all the information about them you need recapped during their appearances if you haven't seen them on TNG, so you won't be totally lost.