I'm an old time Battletech fan and I have decided to join the BT on-line community and I have been kicking around an idea for a grim dark BT AU and I would like some advice on designing a BT AU setting.
Thanks in advance for your input.
I'd say there are two possible approaches you can take to designing it.
Firstly, you can establish a point of departure from canon events and then extrapolate forwards to see how this changes the setting.
For example:
suppose that Andery Kerensky did not die on Eden during Operation Klondike. In order to defuse the rivalry between Clan Wolf and Clan Jade Falcon over who would receive the Kerensky bloodline, Andery suggests that he joins the Jade Falcons and Nicholas joins the Wolves as intended. In the short term this reduces the rivalry but in the long term the two Bloodhouses emerge as rivals. After Nicholas' death Andery is elected as ilKhan (rather than Jerome Winson) and this unintentionally begins a whipsaw effect of the Clans always electing a Kerensky as the ilKhan, alternating between the two bloodhouses and as the differences mount, a schism develops between the two Clans and their respective allies. Once the Crusader issue arises, it becomes a fighting point between the two factions and leads to a short but savage war between the Clans over the issue - a war that wrecks several Clans to the point of absorption.Secondly, you can establish the circumstances you want for the setting and then work backwards to see how this could have been reached.
For example:
suppose you want a circumstance where the Third Succession War ended with the Federated Suns and the Free Worlds League joined forces and crushed the Capellan Confederation between them. How could this happen? Well, we're dealing with Janos Marik and either Hanse Davion, his brother Ian or their father Andrew. Janos became Captain General in 2991 and largely refrained from serious military action so the FWL could recover and also prepared for celebrations of the end of the millennium. As a young and idealistic ruler, possibly he issued something like Katrina Steiner's Peace Proposal. At the other side of that, there's Andrew Davion, who knows he doesn't have much time left and will have to entrust the Suns to his young sons and his son-in-law Michael - who is both ambitious and rabidly anti-Capellan (at least officially) - so while an outright peace proposal isn't feasible he's open to an alliance that could give his sons at least one secure flank. Also, Janos' first daughter Theresa is almost exactly the age of Hanse Davion. Janos was certainly interested in arranging politically useful marriages for his children so possibly the millennial celebrations are held by both states and culminate in the marriage of Hanse Davion to Therese Marik, possibly followed by a dramatic war declaration by the father of the bride and the elder brother of the groom: "In honour of this marriage we give the happy couple a princely prize: the Capellan Confedertion."In both cases, start with an idea and flesh out. From there it depends how you want to present it:
As a scenario, you're mostly outlining the big picture.
As a story, you'd want to figure out who the key characters are and what arcs they'll experience through the story and which events should be told through their eyes, and which would not and therefore need alternative viewpoints for (or if they can be presented as second-hand news).