Julius had become the richest and most powerful man in the Roman Empire. Brutus who was Julius's friend and others among the senate started to fear that this fame and power could lead to a monarchy.
People who called themselves the liberators planned to end Caesar's power by killing him. Brutus was hesitant at first, but the persistent nature of the liberators and the thought of what the future might become, he went along with the plan.
Julius was killed and the public went in an outrage. The liberators left the city. The people who commited the crime locked themselves in the capital. In the end, what they had hoped to stop had become reality.