Augustus Caesar and the Masquerade of the Republic
From a republican point of view, he was a wolf in sheep's clothing.
In 8 BC, this month of August was renamed after Augustus Caesar, the first Roman Emperor. Reportedly, he didn't insist on a month being named after himself. The Roman Senate offered it to him, and he chose this month (then called Sextillis1) because it'd been the month of several of his great victories.
This was very characteristic of Augustus. He didn't demand a month be named after him; he graciously accepted when his flatterers offered it. Similarly, he didn't position himself as a monarch; he ruled informally without the titles and claimed to have protected the Roman Republic. From a republican point of view, to cite a fable already popular in his day, he was a wolf in sheep's clothing.
We call Augustus the first Roman Emperor, because he was. There clearly is a difference between the Roman Republic and the Roman Empire. If you're going to pick a moment when the Republic became the Empire, it's going to be during the rule of Augustus. He even used the title "Imperator," from which we get our word "Emperor." However, he didn't present himself with anything of the pomp we would associate with an Emperor - nobody did, down till the time of Diocletian three hundred years later. Augustus didn't say he was inaugurating a new system of government. He proclaimed that he was restoring the Republic out of chaos and civil war; he was merely an important citizen of the Republic, first-speaker of the Senate holding several important magistracies.
He called himself "Imperator", from whence we get "Emperor" - but at the time, that just meant "general" or "commander". He called himself "Caesar," from whence we get "Kaiser" and "Czar" - but at the time, that was just his name2. He called himself "Princeps," from whence we get "Prince" - but at the time, that meant "First Citizen," the title for the Senator who got to open debates. All these titles would later become monarchical titles, because everyone looked back on Augustus as the monarchical ruler of Rome. But at the time, they weren't. In Rome, with its strong anti-monarchical traditions, Augustus refused to take the title "Rex", or "King", and insisted he was merely restoring the Republic.
But in reality, Augustus controlled all Roman public business and affairs. After winning several civil wars in succession, he commanded and had the personal loyalty of almost all Roman armies, had personally chosen most of the Senate (after most of the previous Senators had died in the wars and purges), and personally administered much of the city of Rome's grain supply. Until a new special magistracy was invented for him, he was Consul and Tribune and Censor and First Citizen and governor of about half of the Empire's provinces. In case this wasn't enough, as a Censor, he could remove any Senator or magistrate.
Augustus was careful to keep control of Roman affairs without technically overstepping his bounds. For example, when the governor of Macedonia3, Gaius Primus, started a private war against the tribes to the north, he was put on trial for illegally waging war. This was all according to the Republic’s law, though he could probably have gotten off if he was politically popular. However, his defense was that Augustus had sanctioned this illegal action. Augustus personally intervened at the trial, denying he'd sanctioned anything like it, positioning himself as the defender of Republican legality. However, shortly afterwards, Augustus had Gaius Primus's lawyer executed for treason. Whether or not the treason was real, the message was clear.
Rome welcomed Augustus because he promised peace and order. After about four civil wars in about sixty years, coupled with continual foreign wars, they sorely needed it.
The first of these repeated civil wars started with Sulla, who while leading the Roman army against Mithridates of Pontus had fallen out of favor with the Senate at Rome. After making a favorable peace with Mithridates and other local kings, in 83 BC, Sulla led his army back to Rome and forced the Senate and assemblies to declare him Dictator - an old and obsolete title which he revived with broader powers. He sincerely tried to reorder and restore the Republic, but he only weakened it more - not the least by his example of violently seizing power.
Then, after about twenty years of peace, the Republic fell under the influence of Julius Caesar and other elite Romans he'd allied with. While Caesar was busy conquering Gaul (in 58-50 BC), their alliance fell apart, and (after Caesar illegally led his army from Gaul across the Rubicon) they fell to civil war. Caesar won the war and intimidated the Senate and assemblies into appointing him Dictator in 49 BC. Caesar stayed Dictator until 44 BC, fighting and winning the civil war against his former allies.
On the Ides of March in 44 BC, Caesar was assassinated by a group of elite Romans (including Brutus and Cassius) who thought he was too powerful to be safe for the Republic. However, a month later, Caesar's supporters (Mark Anthony, and Octavius who would later become Augustus) had gained popularity among Caesar's old soldiers, and the barely-interrupted civil wars picked up again: first Anthony and Octavius against Brutus and Cassius, then Octavius against Sextus Pompey, then Octavius against Anthony in what historians aptly call "the Final War of the Roman Republic."
And then - in 30 BC - Octavius finally won. By then, between wars and purges by the various factions, the Senate was almost empty. Everyone was exhausted. So, when he promised peace and the sheep's clothing of a claim to restore the Republic, they praised him and eventually called him Augustus and named the month of August after him. But, more firmly than Sulla or Caesar or Anthony or anyone else before him, he held sole power.
But even aside from those civil wars, and even without Augustus coming as a wolf in sheep's clothing, the Roman Republic had become inherently unstable.
The Roman Republic never was a republic by today's standards, in more than show - and never even that beyond the area around Rome itself. Power was nominally in the hands of the public assemblies where the people of Rome literally assembled to vote on matters. All (adult male) Roman citizens could participate there. But most power was actually in the hands of the wealthy and respected elite4 - power they controlled by a variety of informal means, such as their prestige, gerrymandering different "tribes" of voters, and longstanding traditions where only people who'd already held some offices could be elected to others.
And then, of course, all this was just for Roman citizens - not for the "socii," or "allies" in the rest of Italy. The socii could govern their own internal affairs, but they were effectively subjects of Rome. They finally got citizenship late in the Republic, but they didn't have a chance to actually enter into Roman power circles until Augustus brought them in to replenish the mostly-empty Senate.
This balance of elite and commoners became unstable several times throughout the Republic, but it became worse as Rome conquered farther-away provinces. Wars kept lasting longer, travel took longer, and armies stayed in the field longer. Common soldiers were no longer back in time for the harvest, or even in time for their family's farm to still be viable. Wars no longer won them viable new land to farm. Many Romans didn't even own farms anymore - the elite, flush off the wealth of Carthage and Spain and Asia5, had bought more and more land in "latifundia," literally "broad farms." By the end, the soldiers fighting in the final generations of the Republic - even before any actual civil war - knew that they didn't have farms or homes to return to.
Early in the Republic, all military commanders had been changed every year if not more frequently. Among other things, this kept any army from getting too loyal to an individual general. However, as their wars got farther-flung, and as experienced generals got rarer after dying in civil wars, they began commanding for longer and longer - and their armies with less ties to civilian life became loyal enough for their generals to lead them into civil wars.
That was how Sulla and Pompey and Caesar and Anthony were eventually able to lead their armies against each other and against Rome itself. That was how, when Augustus came as a wolf in sheep's clothes and ended the Republic, the army welcomed him.
But even if Augustus hadn't done what he had, the Republic was unstable enough it could not have lasted much longer. When Brutus and Cassius killed Julius Caesar to save the Republic, they were much too late.
Augustus was the first of many Roman Emperors. He (with the confirmation of the Senate) bequeathed all his authority to his stepson Tiberius, who bequeathed it to his nephew Caligula. But, if Augustus was the first of this pack of wolves, they also kept his sheep's clothing of Republican rituals. Even as Imperial authority became even more obvious, even as rebelling generals proclaimed themselves Emperor (starting in AD 68, a mere 54 years after Augustus's death) - even then, the Republic was never officially abolished. Each Emperor was, officially, holder of the same offices as Augustus in the name of the Roman Republic.
The Republican institutions also stayed around. The Senate kept meeting until the seventh century, well after the fall of the Western Roman Empire; the Republican assemblies kept nominally meeting until the third century. Even after this, a new Senate persisted under the Eastern Roman (Byzantine) Emperors in Constantinople. Some historians6 argue that these institutions persisted even further: that the Eastern Roman Empire is better understood as a mostly-nominal republic like Rome under Augustus than as a typical kingdom.
There are many points one could point to as the end of the Roman Republic. One could point to the last meeting of the Senate in 603 AD, for the division of Italy into provinces under Diocletian in 284 AD, or to the first successful military coup by a self-proclaimed emperor (Vespasian) in 69 AD. However, it's probably best to say - as most people say - that Augustus put an end to the Republic.
But he was probably the best way it could have ended. If Augustus was a wolf in sheep’s clothing from the Republic’s point of view, then from other points of view, the wolf turned out to be a helpful dog. He re-founded Roman rule on a more stable foundation, while preserving the forms and name of the Republic. And, the end of the Republic being in question points to the complicated nature of Augustus's rule.
Originally, the Roman calendar started with March (the start of the campaigning season, named after Mars the god of war); and continued through April (of uncertain meaning), May (named after the goddess Maia), June (after the goddess Juno), Quinctilis (fifth-month, now renamed July after Augustus's uncle Julius Caesar), Sextilis (sixth-month, now August), September (seventh-month), October, November, December (eighth-month, ninth-month, tenth-month), January (the god Janus), and finally February (the month of the Februa, a purification ritual).
His adoptive name, after being adopted by his uncle Gaius Julius Caesar. His birthname was "Gaius Octavius Thurinus"; "Augustus" was another honorific title awarded by the Senate.
The Roman province of "Macedonia" was, roughly, the northern half of modern Greece.
This was relatively normal at the time. In fact, up into the modern era, the Roman Republic was unusual in even allowing all adult male citizens to nominally vote - most republics were more clearly ruled by aristocrats.
The Roman province of "Asia," or "Asia Minor," is what's now western Turkey.
Such as Anthony Kaldellis in his book The Byzantine Republic. His thesis is controversial, but at least arguable.