How much influence do you have with your DM? Is he willing to alter the map a bit for back-story purposes? Unther is currently in a state just shy of falling apart - Mulhorand has taken most of it, and Chessenta looks ready to claim a bit as well if they get the chance. What if it got the chance a few years prior to the party entering the FR scene? Remove Unther and replace it with lands held by Mulhorand and Chessenta - with a liquid border where they meet (by which I mean that the border is not yet determined, each gains and loses lands here and there along the border on a weekly to monthly basis).
Say that few years ago some charismatic leader arose in one of the more major and militant city states in Chessenta and basically lead that city state into consolidating power over the others - such that they become provinces of the empire whose capital is now in that major city state. This occurred during the Mulhorand invasion of Unther - perhaps even influencing the invasion, as Mulhorand may have hoped that a Chessenta being consolidated by war would be too busy to take any of Unther - or that Unther would be split between fighting off Mulhorand and guarding its borders with Chessenta on the off chance that Chessenta might decide to expand across the border.
Now Chessenta is notably larger than before - having expanded into Unther and some other bordering lands. Mulhorand holds most of Unther, but about a quarter to a third is held by Chessenta, with some cities having been traded between the two several times in the last three to four years.
Your character could have been a youth conscripted into the army as Chessenta consolidated or as it invaded Unther. Or perhaps you were an Unther youth captured as a slave by the invading Chessenta army and - due to strength, or whatever - sold to an arena. Now a year or two later you've won enough fights to have perhaps bought your freedom* and have left this foreign land to explore afar. * (If that is allowed in Chessenta; I cannot recall off hand if it is typical for that culture / region. If not, perhaps you managed to escape the arena and left Chessenta more to escape bounty hunters than to travel).
Does any of this work for you? Would your DM allow such alteration of the setting for a more interesting background?
