Historian: Much of what made medieval European communities as close-knit as they usually were was the way they went about meeting basic needs.
Conclusion (So / probably)
If people in industrialized societies undertook corresponding group tasks, their communities would probably become more close-knit.
Intermediate Conclusion
Much of what made medieval European communities as close-knit as they usually were was the way they went about meeting basic needs.
Evidence
In medieval communities, to get crops harvested or to dig a well, people had to come together in respectful cooperation, despite any private grievances they might have had.
Evaluate
On Main Conclusion and Role, the main conclusion is earlier than the evidence about 85-90% of the time (it's usually the very first sentence or attached to some pivot/rebuttal).
But here we looking at the 10% of the time where the Conclusion is actually the last claim in the paragraph, on a Main Conclusion question. (This tends to only happen on easier Main Conclusion questions early in the LR section, such as Q6 like this one)
We know the word "So" indicates conclusions. The word "probably" often indicates an Opinion. Both of those words show up in the final sentence.
When we think we've found the Conclusion, we should test whether it is actually supported, by asking why should we believe that?
Why should we believe that we modern industrialized societies would probably become more close-knit if we undertook group tasks with the community?
Because ... much of what made Medieval societies close-knit was the group tasks they undertook together (such as harvesting crops or digging a well). It forced them to come together in respectful cooperation, suspending any private grievances.
Goal
Okay, we confirmed that the last sentence is the conclusion. It is wearing a conclusion indicator (So); it is expressing an opinion the author has (probably); and it is supported by the other two claims in the paragraph.
So let's go find an answer that matches the meaning of the final sentence.