What marked the end of the Roman Republic?

The end of the Roman Republic is marked by the transition to the Roman Empire, which officially began when Octavian (later known as Augustus) became the first emperor following the defeat of Mark Antony and Cleopatra in 30 BCE. This shift represents a structural change in governance from a republic, where elected officials represented the people, to an imperial system consolidated under a single ruler.

The assassination of Julius Caesar is a significant event in this timeline, as it highlighted the political turmoil and conflicts within the Republic that ultimately contributed to its downfall. However, it did not directly mark the end of the Republic itself. The founding of Rome occurred centuries earlier and is not linked to the end of the Republic. The fall of the Western Roman Empire in 476 CE is also a later event, unrelated to the transition from the Roman Republic to the Empire. Thus, the transition to the Roman Empire encapsulates the definitive shift away from the republic's political framework, making it the correct answer.