Explanation: Octavian, later known as Augustus, was the grand-nephew and adoptive son (posthumously, by will) of Julius Caesar, of conqueror and dictator fame. Caesar was, famously, assassinated by the Senate, including by many Senators he had pardoned during the civil war, despite them taking up arms against him.
When it became apparent that the assassins of Julius Caesar had little support amongst the people of the city of Rome, they fled to the east and tried to raise an army to retake power (they would lose the ensuing, second civil war), while the 'moderate' conservatives who had only cheered on the assassination, not participated in it, tried to negotiate with Caesar's supporters for some sort of reasonable accord to preserve their power. Of the 'Second Triumvirate', as they became known in historiography, Lepidus was a no-one, and Mark Antony was a brute who would have cheerfully executed every Senator who spoke out against him if he could have gotten away with it. Luckily, Caesar's grand-nephew, so young and impressionable, was willing to work with the Senate towards a reasonable future
Unfortunately for the oligarchic Senate, the deeply cunning and manipulative Octavian had no intention of being their champion. Unfortunately for the Republic, he had no intention of being the champion of the democratic People's Assemblies of the Roman Republic either. Instead, Octavian consolidated power and quietly sidelined (and sometimes executed) rivals until no one was left brave enough to openly oppose him. After his military victory over Mark Antony (who had allied himself with the Egyptian Queen Cleopatra during this third and final outbreak of civil war in Octavian's lifetime), Octavian/Augustus made it clear, if only implicitly so, that there was no more power in the Republic without his say-so.
'Funny' enough, the Republic was not formally abolished after this, and Augustus, publicly, kept up the pretense that he was just a really special boi who had come into all these crazy offices of ultimate power with indefinite term lengths basically by accident during a period of crisis, just normal Republic things! After all, would some aspiring autocrat insist that he was merely the First Citizen, and First Amongst Equals? (Princeps and Primus inter pares)
The Romans would struggle with this split between reality and theory for the next ~300 years of what-we-now-call the Roman Empire, sometimes acknowledging the Emperor as autocratic, other times insisting that no, there was TOTALLY still functioning republican institutions, and that the Emperor was JUST the First Citizen who was a mouthpiece for the Senate and PEOPLE of Rome! Nothing to see here, folks! (Most elite writing took a view somewhere in-between these two extremes, acknowledging the Emperor was crazy-powerful to the point of dictatorship, but still envisioning the position of Emperor in basically magisterial, republican terms)
Also, the map is inaccurate, as that's the 117 AD map of the Roman Empire, which had a few more bits and pieces than it did in Octavian's time. XD

