Complex sentence: Elam asks Cullen if he has, to which Cullen does not reply, and goes to drink with Johnson, who tells him during conversation that the Civil War caused him to cross moral boundaries he did not think he could.
Split into simpler sentences: Elam asks Cullen if he has, to which Cullen does not reply. While presuming to drink with Johnson, Cullen listens to him explain that the Civil War caused him to cross moral boundaries he did not think he could.