HISTORY:
In past years, the Commonwealth of Magi was a strong city-state in the Northlands, twixt the forests of Wesmere and the Wild Steppes and including some territory in the mountains. The harsh weather was somewhat moderated by the seas presence, and the people prospered, working some of the greatest spells ever created. However, massive orc attacks slowly sapped the unity and strength of the Commonwealth, and its capital was abandoned in the year 406. Indeed, the present-day orc city of Glamdrol lies not far from its ruins.
However, the destruction of the Commonwealth as an organized political entity did not stop it from existing. In the present day, the Commonwealth exists more as a loose network of mages and their guards in several major cities throughout Wesnoth, capable of banding together when threatened as a whole. Although all of the Commonwealths mages are ultimately loyal to the Commonwealth, they oftentimes take on the political leanings of their home region, and will assist the established government in day-to-day affairs.
In combat, the Commonwealth depends mostly upon magic. Its magicians are among the best in the world, a legacy hearkening back to its days of glory. Alchemy is also an established art among the Commonwealth, and the products of alchemy are perhaps more successful at war than at peace. Mindful of the lessons learned at the hands of the Orcs, they also maintain a small standing army and an alliance with the majestic birds of their former home.
Their fighting style is somewhat different from that of most human armies. Expertise in combat magic means that mages and alchemist become the primary means by which the Commonwealth armies do battle: all else is there simply to prevent the mages from being interrupted by a sword in the face. Despite this, those who underestimate the Commonwealth military are in for a rude surprise. 

CREDITS:
The primary thing to credit now is the art. All of the art that looks decent was borrowed from existing campaigns or the Images Gallery, under the GNU GPL.
The base sprite for the Journeyman series was taken from the images gallery. It was originally found in Xan's contrib page, but I have seen the same image in other pages too. If the original composer wishes credit, contact me by PM at the Wesnoth board.
The sprites for the Loremaster/Seeker are taken from the Aragwathi, in the Extended MP Era. They were originally done by none other than Wayfarer.
The sprites for the Roc series are courtesy Ringcaat, from his campaign A Gryphon's Tale.

I would also like to thank the community of the Wesnoth board by accepting my rough idea, not pelting me with fruit in various stages of decay, and helping out with my WML problems. The tutorials under Create were very helpful, and I reccomend them to anyone who wants to take a crack at this.

A last note, that I'm not sure where else to put: I am getting seriously out of my depth here. I would welcome any sort of advice or help someone more experienced than this could provide.