The Roman Republic was founded in 509 B.C.E. after the last Etruscanking that ruled Rome was overthrown. Rome's next government served as a representativedemocracy in the form of a republic. Initially, Rome's wealthiest families, the patricians, held power and only they could hold political or religious offices. Everyone else was considered plebeian, and no member of this group could hold office. Over a period of nearly 200 years, however, the plebeians fought for and gained power within the government.

At the heart of the Roman Republic was the Senate. The Senate advised on matters pertaining to rules governing the city and population. In the republic, members of the patrician class served as advisers to the other governing bodies of the republic. Although the Senate did not formally make laws, the prestige of its members gave the Senate great influence over Rome's law-making bodies.

The Senate lasted as the sole governing body for the republic for only a brief time, lasting from the republic's founding in 509 B.C.E. until 494 B.C.E., when a strike orchestrated by the plebeians resulted in the establishment of the Concilium Plebis, or the Council of the Plebs. This gave the plebeians a voice in the government. As a result, new legislative, or law-making, bodies of the Roman Republic were formed. Called assemblies, these legislative bodies shared power in the following ways:

• Comitia Centuriata — This body decided about war, passed laws, elected magistrates (consuls, praetors, and censors), considered appeals of capital convictions, and conducted foreign relations.
• Concilium Plebis — This body elected its own officials and formulated decrees for observance by the plebeian class; in 287 B.C.E., it gained the power to make all decrees binding for the entire Roman community.
• Comitia Tributa — The tribal assemblies, open to all citizens (who only could be free, adult males.), elected minor officials, approved legislative decisions often on local matters, and could wield judicial powers but could only levy fines rather than administer capital punishment.

Leading the republic were two consuls who were elected by legislative assemblies. They served for one year, presided over the Roman Senate, and commanded the Roman military. Though their power was somewhat limited by the establishment of other magistrate positions, the consuls were effectively the heads of state.

The republic stood strong for several centuries. However, as Rome's power and territory expanded, internal conflicts began to emerge as citizens and families struggled for power. For example, in the first century B.C.E., the famous Roman orator Marcus Cicero uncovered a plot by a Roman senator, Lucius Catiline, to overthrow the Roman government. Some citizens, such as the Gracchus brothers, attempted to institute government reforms and social reforms to help the poor. Ultimately, factions emerged (loyal to either the patrician or plebeian classes or to a specific military general), hostilities erupted, and a series of civil wars plagued the republic. During these civil wars, a prominent general and statesman named Julius Caesar began gaining significant power. He commanded the loyalty of the soldiers in his army and enjoyed access to substantial wealth after conquering the province of Gaul.

The Senate, fearful of Caesar's power, demanded he give up command of his army and return to Rome as a citizen. Caesar refused, instead marching his army south directly into Rome. As a result, another civil war erupted between Caesar and his chief political rival, Pompey. Caesar emerged victorious and was named dictator for life. Previously, the title dictator was given to an appointed, and temporary, leader in times of military emergency. Other leaders within the republic feared Caesar would become a tyrant with this new title. To prevent this, a group of senators conspired and assassinated him. In response to Caesar's death, his nephew and heir Augustus defeated the conspirators. He then established himself as the first Roman emperor.

The Roman Empire dramatically shifted power away from representative democracy to centralized imperial authority, with the emperor holding the most power. For example, under Augustus's reign, emperors gained the ability to introduce and veto laws, as well as command the army. Furthermore, the emperor wielded significant authority over those who served in lower-level executive positions. No citizen could hold office without the emperor's consent. As a result of this redistribution of power, the popular assemblies that functioned during the republican period became less important and lost power.

While the assembly became virtually ceremonial, the Senate survived. Primarily, the Senate survived during the early period of the empire as a legitimizer of an emperor's rule. The powers given to the emperor still came from the Senate. Since the Senate was composed of Rome's elite and intellectual citizens, they affected public opinion. With this power, the Senate could declare an emperor to be an enemy of the state, or following an emperor's removal or death, the Senate could officially wipe the record of his reign from official history.

At the time of Augustus's reign, the Roman Empire had solidified control over the Italian peninsula, established North African colonies following its victory over Carthage during the Punic Wars and controlled large swaths of territory in Spain and Gaul. Under the emperors, Roman territory expanded farther, dominating most of the European continent, including Britain and major areas of modern-day Eastern Europe.

This expansion, while bringing to Rome great wealth, power, and prestige, ultimately helped bring about its downfall. Even with the Roman road system contributing to the mobility of the military and trade, the cost of maintaining the vast empire weighed heavily on Rome's treasury and its political administration. Added to this burden were increasing raids and attacks by foreign tribes and communities. Emperors attempted to solve these problems through internal reforms.

For example, the emperor Diocletian split control of the Roman Empire into two halves, a western and an eastern portion. Diocletian believed the territories throughout the empire would be easier to control and support if they were overseen by two administrations. Future emperors attempted similar reforms, but ultimately internal conflict between the eastern and western halves, external pressure by foreign tribes, and the ongoing depletion of Rome's wealth and infrastructure finally rendered the empire vulnerable to collapse.

In C.E. 476, the last of the western Roman emperors, Romulus Augustulus, was dethroned. Nevertheless, the eastern half of the Roman Empire, identified in history as the Byzantine Empire, would last another thousand years falling to the Ottoman Turks in C.E. 1453.