Answer:
When the Romans drove out the Etruscan monarchs and established their own government, the Roman Republic was born in 509 B.C. As a result of seeing the issues with monarchy in their own country and with Greek aristocracy and democracy, they chose a blended system of governance with three branches. Romans felt their mixed system of government will equalize the authority of the two consuls, the few, and the many. They did this out of a sense of individual freedom and peace. Because it incorporated the benefits of monarchy, aristocracy, and democracy in a way that prevented authority shifts and the inevitable rise of tyranny, Polybius believed that this system would be successful.