Alternate History by Causality

Working out an alternate history timeline can be a daunting task. There are any number of points of divergence to choose from, and it's easy to go down a rabbit hole of possibilities. Throw in alien space bats, and the potential plots are absolutely overwhelming.

One way writers handle this is by writing 'steered' alternate history. These works get us towards a specific outcome, and move from the original point of divergence (which can be in the backstory or in the plot of the work itself) towards a pre-determined outcome. Stories like this can work very well, especially when the planned outcome serves to make a point (the mocumentary Confederate States of America makes excellent use of this). And it can be just plain fun, particularly if you have a specific alternate world in mind. It's even possible, as Confederate States of America did, to set your story well after the event that serves as the point of divergence.

At the same time, steered alternate history presents several challenges. First, it requires a light touch so that the outcome seems natural, rather than contrived. Second, it's important to have a clear idea not just of where you're going but why. Third, even if they never make it to the page, it's important to plot out all the intervening events between the point of divergence and your end 'goal' so that you have a cohesive world. You may also need to reference these events in unexpected ways as the story develops.

Because I'm a data scientist, and fixated on causality, my preferred method for plotting is to use counterfactual history techniques. While this is generally seen in 'hard' alternate history, it can still be applied to alien space bat scenarios (Michael and I being firmly in alien space bat territory). It's important to note that this means your story will be largely 'unsteered', with the plot determined almost entirely by causal events stemming from the original point of divergence. The advantage to this approach is that it centres on plausible cause and effect relationships, so there's a lower risk of your scenario seeming contrived. Plus it can be a good tool for exploring questions about history and society in a realistic way, rather than presenting a more conclusive answer.

In summary, both approaches require a similar amount of research, and a similar amount of plotting time spent on the course of the plot after your chosen point of divergence. In the end, I'd recommend the second technique for capturing that event, and the second for a story which looks exclusively at the (perhaps distant) aftermath.