What is the immediate cause of brutus' suicide?

Brutus' suicide in Shakespeare's "Julius Caesar" is immediately prompted by his defeat at the Battle of Philippi. Facing the overwhelming forces of Antony and Octavius, Brutus realizes that he and his allies cannot win the conflict. To avoid capture and the dishonor of defeat, he chooses to take his own life, believing it to be a more honorable end. His suicide reflects his principles and the tragic consequences of his actions throughout the play.