What are some of Caesar's actions in Julius Caesar that show ambition?

Julius Caesar showed he was ambitious by marching on Rome when Pompey was in power and then defeating Pompey’s army in the civil war. Caesar felt he was in the right to do this because he felt Pompey was abusing his power, but it was considered a very unnecessary and brutal action by many of Rome’s important citizens.

Shakespeare shows us the importance of Pompey's defeat — and the triumph that followed — through Marullus’s...

Julius Caesar showed he was ambitious by marching on Rome when Pompey was in power and then defeating Pompey’s army in the civil war. Caesar felt he was in the right to do this because he felt Pompey was abusing his power, but it was considered a very unnecessary and brutal action by many of Rome’s important citizens.

Shakespeare shows us the importance of Pompey's defeat — and the triumph that followed — through Marullus’s speech to the craftsmen in the first scene.

And do you now strew flowers in his way
That comes in triumph over Pompey's blood? Be gone!
Run to your houses, fall upon your knees,
Pray to the gods to intermit the plague
That needs must light on this ingratitude (Act I, Scene 1).

Cassius convinced Brutus that Caesar was ambitious and determined to become king. It was not difficult to do, as Brutus was unhappy about the incident with Pompey. The incident at the Feast of Lupercal just served to reinforce the conspirators' fears. Mark Antony offered a crown to Caesar three times. He refused it three times, but Brutus and Cassius felt the incident seemed staged.

BRUTUS

What means this shouting? I do fear, the people
Choose Caesar for their king.

CASSIUS

Ay, do you fear it?
Then must I think you would not have it so (Act I, Scene 2).

Caesar is certainly ambitious. He is also arrogant, as shown by the way he refuses to listen to the soothsayer's warnings or read Artemidorus's letter. Caesar also doesn’t listen to the suit brought by the conspirators, in which they try to get him to pardon Publius Cimber. Caesar basically tells them that when he makes a decision, he sticks to it. This refusal to listen only reinforces the idea that Caesar is dangerously arrogant.