Brutus’ downfall was his own doing. He participated in Caesar’s assassination out of his own volition. He was not forced to participate, but he was convinced to by Cassius. Brutus's participation was fueled by his personal fear of Caesar’s growing ambition and the threat Caesar posed to the continuity of the republic. His participation in Caesar’s assassination initiated a series of events that eventually led to his own death.
After Caesar’s death, Antony’s speech stirred the public against the conspirators and into action. The public was ready and willing to get rid of them just as they did their beloved Caesar. This situation forced the conspirators out of the city. It also led to the establishment and rise of the second triumvirate and a battle between the conspirators and those who supported Caesar. The battle eventually led to the death of both Cassius and Brutus.