What marked the official transition from roman republic to roman empire?

So in the first century of BC, Rome was a republic -- but eventually, senators began fighting for power between themselves and the republic soon fell into chaos. Two men, one of which were Julius Caesar, were able to wrestle Rome back from chaos and rule in their empires. Though he was murdered and his rule was brief, it marked the official transition from Roman Republic to Roman Empire.

Iwould have to say c. the german americans.