An aspect of alternate history that is often misunderstood, or overlooked, is that the removal of a nation’s ability to act is not the same as their choosing not to act.
If in reality, country A had the choice of whether to carry out an action or not, and chose to do it, if in the alternate history they are no longer in the position to act, whether they want to or not, the outcome does NOT resolve to what would have happened in reality if they had chosen not to act. The fact that they still had the choice to act would have coloured other nations’ own actions and responses, but the removal of their ability to act would mean that other nations no longer have to take them into consideration when considering their own actions.
As a hypothetical, Britain intervenes in the chaotic situation inside a country within their sphere of influence. The alternative to their not intervening is either that civil war breaks out, or that some neighbouring state intervenes. Now, take an alternate reality where Britain is not able to intervene even if they wanted to – here, France, for example, might step into the breach because, in this ATL*, France is not stepping on Britain’s toes but making the decision to get involved based solely on its own merits.
The absence of the choice to act, rather than the choice not to act, brings a different dynamic to these situations and allows nations that historically did not consider acting to do so, or ones which would have wanted to, but knew better than to push things, to make their move.
This is a type of butterfly which is often overlooked.
I go into a bar and hit on a girl, and the options are either her boyfriend hits me, or we sneak out the back. Sans boyfriend, maybe we make out there and then, or maybe she rejects me but I stay around. Think of that in nation terms, in terms of recognised spheres of interest, in terms of satellites, vassals, protectorates, or native states who have treaties with one power. Absent that power, and the choice for other powers is no longer the same – the door is opened to them to act where they would not usually have dared. They may fail, but even in failing they have a larger presence going forward than the power who is, in this ATL, absent from the calculation.
Also, the perspective can be turned around. Look at this from the point of view of the native state, or minor state, which historically always had to consider the effect of its actions upon a larger power which claimed pre-eminence. If that power is absent then there will not be a vacuum. Either, the native state is able to fill a sufficient proportion of the void to gain for itself significant freedom of action, or another power has stepped into the void to attempt to impose its imperial will.
Or, perhaps more likely, there is a combination of assertive native state and ersatz imperial power, seeing a stronger and more virulent native state going forward under the protection, or aegis, of a different power. This could be a subservient relationship, or more one based upon a proper alliance, but placing the native power clearly enough in the orbit of its ally.
Whilst in a hypothetical discussion such things as these can seem obvious, upon reading, in terms of alternate history discussions they are often overlooked, or ignored, or condemned by people whose minds cannot handle the new situation. People get a narrow tunnel vision that says that in such-and-such a situation the ONLY choices were A or B, whilst forgetting that if the major power is now absent the entire dynamics of the choice are altered.