OK, so I didn't want to try and put this in for a lunch post, as I was looking at Ruwin's character. But here goes.
The commonly known recent history of this continent is tied inextricably to the term "shifter." For the common folks in the taverns and farms of the continent, or the businessmen just trying to make a living, a Shifter is a perverter of the natural order, a menace to them, a danger to all that is right with the world. It's a broad term, therefore, and prone to wide variations of subjective application. That is what makes it such a dangerous term, as opposed to "Necromancer" being a very narrowly applicable term that leaves no doubt of what it means. Many a mage or other misunderstood group has been unjustly labeled shifter and rejected, persecuted and/or hunted to a final, bloody end. It holds an icy, powerful grip upon the psyche of the inhabitants of Castelon because of the far-devastating effects of the two Demon Wars on the continent.
In terms of history, the second Demon War that embroiled the continent was set forth in motion by a network of shifters that summoned very powerful demons, believed to be high servants of the demon princes. The reasons for this are assumed that they are cultists of these demons. The results of the war were very different for the major population groups on the continent. The two most devastated realms were in the north, the Spiritfolk of the Western Kingdoms and the Forestfolk of the Mystic Wood.
The home of the greatest sources of divine worshippers on the continent devoted to Pelor, the demon-led armies naturally struck out to eradicate the Western Kingdoms, and very nearly did, ruining the armies of all four kingdoms and their central, shared Holy Army of Carthayne. After the war ended, three of the weakened four kingdoms then fell steadily to predations from determined shifter forces, leaving but one surviving holy realm left.
The Forestfolk of the Mystic Wood are the continent's most mysterious, cloaked peoples. Only a few know truly of the centers of power within the forest realm, commonly rumored to either be a druid council, or circle of elders propped up by druids, depending on who you talk to. Few people know of the true reasons why the Demon led armies struck against this hidden realm of people and the native Faeriefolk of the continent, but are believed to be in possession of powerful, deadly, and possibly sinister secrets that forced them to lock themselves away from the rest of the continent. There are many from Southport that did go north to fight the Demon armies, and so there are plenty of firsthand accounts of the bloody attrition of the battles throughout the entire depth of the forest, but few have a clear picture of everything that happened due to the closed, secretive nature of a forest. Common rumors are, though, that a terrible price was paid in beating back the assault, and all contact was lost with the Forestfolk shortly after the war, leading many to think that the war is still being fought in some way under the boughs of that torn land.
Located in the upper north of the continent lies the Northern Realm, the home of the Elementalists, led by the Council of Elements, an open magocracy. Caught between the Western Kingdoms and the Mystic Wood, the two main thrusts of the Demon armies, the realm was active in the defense of both realms, but was ultimately itself overrun. The capital city of Gardan was abandoned by the population of the Northern Realm, and most of the population took refuge in the harsh mountains that run through the center. Gardan itself was razed to the ground by the Demon Armies as they moved forward to assault the Mystic Wood. The Council of Elements itself, and their isolationist mages banded together and were critical in the defeat of both Demon-led armies, and the politically active council was the main reason why the continent was able to muster its forces in time to win the war through their passionate but fair leadership in negotiations during the critical months before the Demon Armies set out northward from the southern Western Spine strongholds.
Though the Southlands of the continent were largely left alone for whatever reason, three separate city-states were overrun and destroyed in the long march north from the southern mountains of the Western Spine. The city-states were part of a loose confederation of city-states that banded together to take in refugees from all of the realms that were shattered, and to defend the Mystic Wood. Southport is the chief leader of this loose confederation, and has taken the brunt of shifter predations in the south since the war, her army and navy weakened considerably in the war. The psions that survived the defense of the Mystic Wood that are now protecting Southport have been very active in combating the shifter threat, but have paid a bloody price nonetheless.
The main battle fodder for the Demon armies were the Goblins of the Western Spine and the Troll Tribes of the Southlands, along with the bands of shifters and their servant abominations and legions of undead. The Goblin Kingdom in the Western Spine is little known in the east, but is known to be older than any human settlement on the continent, and the Western Spine Goblins are far more powerful, organized, and prouder than any goblinoid sub-race in other parts of Aber-Toril. No one knows why, but they also possess a strange magic unique all to their own and craftsmanship and discipline to rival any human kingdom. Few people know what has happened to the Goblins after the war, but it's believed they weren't all destroyed, and are licking their wounds in the relative safety of their mountain strongholds.
Yet through it all, the fear of shifters has caused many rifts in the organized races of Castelon, the Spiritfolk believing that the psions of Southport in particular and many of the mage clans in the southern city states to actually be shifters themselves because of the ruthless tactics they used against the shifters they battled. The enmity of these two peoples hindered the Southlands from being able to help the Western Kingdoms at all, and might have ended differently than with the almost utter destruction of the Western Kingdoms if not for the ingrained distrust and paranoia rooted in the application of that omni-present, derogatory label of shifter.
As to what the shifter goals are after summoning the demons, if there is any central organization and goals at all, and the particulars of the war (the main heroes and villains and their roles in the most recent war), or more importantly what the role of shifters in the war were, that is not something that is widely known, or understood, so that would require having heard information from those rare few that have the pieces put together, and you would have to roll for your Bardic skills to have picked up some of the that information in bits and pieces.
So, I will need to have you do a bardic knowledge check if you are going to learn more to know how much you picked up in your travels through the war-exhausted lands of Castelon.
Another person in the group that might know more than the average traveler is Leana, due to her association in the Spellsword organization, a group of mercenary wizard-warriors that pay very close attention to all the events across Toril so that it can take advantage of opportunities to keep work coming in. If Leana has spent any time learning about the continent, I will allow you to make a single roll that will have a bonus associated with it due to the organization's central knowledge shared with her members.
"Are you sure you want to do that?" - Most important question I can ask you as a DM. So pay attention!
http://www.opengamingfoundation.org/srd.html (3.0 SRD)
http://www.d20srd.org/ (3.5 SRD)