The scene in which the townsfolk agree to give the railroad workers some land to homestead in exchange for their help:
Olsen Johnson: All right, we'll give some land to the niggers and the chinks...but we don't want the Irish!
Bart: (assess the railroad workers reaction) ...No deal.
Olsen Johnson: Aw, prairie shit! (smiles) Everybody.
(everyone happily rushes forward and starts shaking hands like old friends)
- Also, the fact that the black and Chinese workers refused to accept the deal until the Irish were included.