Motive relation

So at a high level, I would ask "what is the author trying to do by including this" and I would indeed come up with something like your pre phrase. If I didn't know impetus there are still a few tools we could use. First, from context we could guess that "help explain the something for the readjustment movement" likely does fit decently well with your prephrase. Second we can use process of elimination: and D has a major major problem. We just don't know anything about the motive of the individual agents. The right answer must have some support in the passage and D really just doesn't.

Thank you!!!