As Tom says, great resources.
And as ever from the historians, questions rather than answers:
How long do the students get to complete the task? (I'm curious, don't necessarily think it matters).
How are the students prepared for the assessment? Do you tell them about WILF?
I think there has been some great thinking and tons of effort put into the assessment. What follows is to help discussion in the context of the work.
The substantive question is "What were the causes..." and the mark scheme focuses on other criteria. In our portfolio world, isn't it possible to think differently and mark on how well the students discuss causation? Viz linked, classified, prioritised... To quote from the New Level 7: "They use these links to analyse relationships between the diverse features of a particular period or society, and to analyse reasons for, and results of, events and changes."
You might even consider changing the question (a la [au?] Lomas) possibly "Could the Civil War have been avoided?"
You could (again a la Lomas) then have staging posts provided to help them find their way to a high level (a handful, lifted from Lomas again...)
Given the situation, what choices might X have had?
Given these choices, what decision would you have taken?
If this appears to have been the best response, why do you think X took this course of action?
Why might X not really have understood what Y was doing/believed in?
What experiences could X look back on the help them decide about…?
The mark scheme you have is a wonderful resource inasmuch as it provides a clear overview for teachers (including non-specialists) of what the various levels 'look like'. I'm sure my department would be very jealous if I ever were to tell them such things were possible!
Hope this is of use. But feel free to cast into the abyss....
A child of five would understand this. Send someone to fetch a child of five. - Groucho Marx