The Sith-Imperial occured from 127-130 ABY and resulted in a reborn-Empire. Darth Krayt played a crucial role in this, and soon he would be the Emperor. So this event happens about 87 years in the future from the book Betrayal. So Luke Skywalker is probably dead. Kol Skywalker gets killed during the Massacre of Ossus, and his son Cade managed to revive his master Wolf Sazen with Force Lightning. He then escapes and becomes a pirate. Both Jedi and Sith are searching for him.
The Empire has always been around since Emperor Palpatine created it. It just hasn't been dominating the Galaxy until they got help from the New Sith Order, which originated on Korriban. We don't know how the NSO (haha) came to be, we just know that Krayt founded it.
Krayt is not Jacen, I must note. He was 10-years-old by the time of the Betrayal books.
With the Jedi Purge at Ossus in 130 ABY, the teenaged Cade almost lost his Master and felt his father die in the Force. On the brink of the Dark Side, Cade plowed a starfighter through the Imperial TIEs to clear a path for the escaping Jedi ship that had the remaining Padawans and his Master on board. The ship was destroyed, but Cade survived.
He became a bounty hunter and was quite formidable 7 years after his father's death. Hasn't used a lightsaber yet, that we've seen, however. He doesn't want anyone to know he's a Skywalker, really.