In Act IV of "Julius Caesar", what lingering effects does the quarrel between Cassius and Brutus have?
The quarrel between the two leaders forebodes their eventual failure. Although they reconcile in this scene, their distrust of each other and their verbal attack on one another suggests the inadequacy of their leadership. If they can not work together as a pair, how will their armies work together to foil Octavius and Antony? This scene directly follows a scene portraying Octavius and Antony making clear plans, which we learn are successful.
In addition, the quarrel between Brutus and Cassius ends with Cassius' concession - he will go to Phillip with Brutus' army, even though he believes it is a mistake. This is the second time that Cassius concedes to Brutus, the first being when Brutus refuses the plan to kill Antony. Both times, Cassius is right and Brutus is wrong. It is directly following their confrontation that Caesar arrives as a ghost to warn Brutus about appearing and Phillipi. Brutus, feeling that his fate is sealed, continues to go forth with the plan. The final effect is the suicide first of Cassius, and then of Brutus.