The Question and Answer section for Julius Caesar is a great resource to ask questions, find answers, and discuss the novel.
They feel that Caesar is becoming too powerful and the republic of Rome will only suffer under one man with ultimate control.
Brutus was an individual who was lured by the conspirator’s arguments about Rome needing to be a republic. In that sense Brutus's decision to betray his friend Caesar was initiated by the combined effort of the conspirators.
Anton is devastated by Caesar's death, but he also sees it as a way to gain political power. Caesar was his friend and leader, but Antony will quickly move on and use Caesar's murder to his own political advantage.