I can understand the impulse to vote to close any new question about the use of whom as a duplicate, since most of them are. However, I don't think that any two questions about whom are necessarily duplicates of each other: we ought to take care to link questions that are actually asking about similar situations.
I think people neglected to do this when ""...will divide the people (who/whom) most need to be brought together"" (formerly titled "Tricky who vs. whom question") was closed as a "duplicate" of "“Whom” or “who” for object of a subordinate clause inside a relative clause" (which is itself (correctly) closed as a duplicate of "The use of nominative "whom"").
The question "“Whom” or “who” for object of a subordinate clause inside a relative clause" deals with a complicated edge case where "who" is traditionally preferred, and by prescriptivists considered the only grammatical option (although some descriptivist grammars such as Huddleston and Pullum disagree and say that "whom" should also be considered grammatical in this context for certain speakers). An answer talking about this complicated topic is mostly irrelevant to the question of whether "who" or "whom" should be used in sentences like "With a two-party system, our nation will divide the people (who/whom) most need to be brought together."
I realize Simon Kuang says "I feel like it should be "whom" as it's the object of the main clause", but if you look at the pattern of bolding in his question, it seems to me that this was actually a mistaken or confused way of saying "not the subject of the relative clause":
I feel like it should be "whom" as it's the object of the main clause.
The interviewed several candidates whom he thought had the experience and qualifications he required.
In any case, John Lawler's answer doesn't seem to directly address the matter of case assignment not being based on the role of the antecedent in the main clause.
So I think the current situation of this question being marked as a duplicate of "“Whom” or “who” for object of a subordinate clause inside a relative clause" is not very good. For this reason, I have voted to reopen "...will divide the people (who/whom) most need to be brought together"; if people think it ought to be closed, I would suggest marking it as a duplicate of some other question, like the general question What’s the rule for using “who” and “whom” correctly? or some more specific question that is actually about the same kind of situation like "a patient who is" or "a patient whom is"?
If a moderator feels it is sufficiently uncontroversial, I suppose I would also be satisfied with the duplicates list being edited to add one or more of these questions (I'd prefer it is the "“Whom” or “who” for object of a subordinate clause inside a relative clause" question was actually removed from the duplicates list, but I can understand that a mod might not want to take that action unilaterally).