Dwarves, Barbarians, Slavers, & The Remains of Empire - Castles & Crusades Greyhawk

If we look at Autarch's By This Axe as the basis for a campaign set on a Mythical Earth then we've got the Dwarves builting a Dwarven empire's infrastructure and basis. 

These Dwarves were created to guide mankind and by the time the adventurers are ready to explore. The Dwarves are on the decline and on thier way out. The Chaos races however are on the upswing. And this leads the Dwarves back into the spot light. This might be because of the fact that the Slavers organization has been pushing the world into full war! 
And this could well be happening at the end of the late Roman Empire. Tribes of human barbarian and forgien warriors are picking at the bones of the Empire. 
The humanoid races are subcombing to the powers of Chaos which are on the rise. 
The Slavers have been stoking the fires of war by doing raids and the constant taking of slaves. These raids have been fueling the collapse  of the remains of the Roman empire. 

According to the original Scourage of the Slave Lords wiki entry; "The original series consisted of four modules:

• A1 Slave Pits of the Undercity
• A2 Secret of the Slavers Stockade
• A3 Assault on the Aerie of the Slave Lords
• A4 In the Dungeons of the Slave Lords

"Each module is a self-contained adventure that leads into the next in the series. The series is intended for use in the World of Greyhawk, but can be imported to any campaign setting."
This means that Greyhawk's Highport and Drachensgrabs regions are going to be at high risk and the PC's are going to have to destablize the Slavers organization from the inside out. And on Greyhawk A1 Slave Pits of the Undercity take place right around the same time as the collapse of the Roman empire so this puts events at 
 580 CY;"The events of the adventure are set in 580 CY, following four years of raids by slavers on the coastal population along the Sea of Gearnat from Onnwal to the Wild Coast. Local lords, finally tired of the situation, hire a band of adventurers to attack the slavers in their home. The adventure begins in the Pomarj city of Highport at a ruined temple which serves as a headquarters for the slavers.^[1] The module takes the group through the temple and into the sewers below where giant insect-like creatures make their lair along with the slave lords." 
And there are deep ties between the barbarian tribes of Greyhawk and the Germanic tribes of Earth. Even though the human tribes can not abide the humanoids of Greyhawk. 
And this goes back to the fact that we're taking full advantage of the Castles & Crusades Codex Germania. 

So what does this mean for PC's?! It means that we're going to have a mix of both Greyhawk and Mythic Earth PC's thrown into a party who are going to be working to escape the slavers. And all of this ties back into A1 Slave Pits of the Undercity. And the simple hook of looking for stolen family members ties events back into 

A2 Secret of the Slavers Stockade.