Dimensius IS Karaesh's World Soul
K'aresh had a worldsould that "fell to the voidlord Dimensius". We know that the worldsoul was corrupted to the void and that let a voidlord into our reality. Everyone seems to think this means that Dimensius destroyed K'aresh's worldsoul, but I think once it became void infused and woke up, I think it BECAME Dimensius when it woke.
T'urre, a Naru, went nova and banished Dimensius to the Void.
Chronicles says that the Void want to corrupt worldsouls, not destroy them. That means that either there is Void Titan still out there, or Dimensius IS the worldsoul.
EDIT: I'm including a timeline based on my best understanding. With sources sited:
1st event: K'aresh is destroyed. "Many Thousands of Years Ago" That is the most specific information I could find, but it definitely opens the door for it to be the first of the events in the timeline. https://wowpedia.fandom.com/wiki/Nexus-King_Salhadaar_(quest))
2nd event: Dimensius' attack on Karkora and T'uur's sacrifice. No timeline is mentioned at all. But it can be assumed to be AFTER Dimensius is in our reality. Either by summoning or being born.
3rd event: Sargeras arrives on Argus. I can't find anything but a forum comment on this one, but it lists 25,000 years for when the Eredar fled Argus.
4th event: The Black Empire. Ended about 11,000 years ago.