The Battle of Philippi was part of the Wars of the Second Triumvirate. It was fought between the army of Octavian and Mark Antony and the forces led by the tyrannicides (those who conspired to murder Julius Caesar). It ended in victory for the Second Triumvirate and consolidated their control over the territory of the Roman Republic. It also witnessed the suicide of Brutus and Cassius, the two main rivals to the political hegemony of the Second Triumvirate.

Gaius Marius was a Roman consul towards the end of the history of the Roman Republic. He was elected as consul an unprecedented number of times and was instrumental in the transition from the Roman Republic to the Roman Empire. Specifically, Gaius Marius is notable for the successful reforms he made to the Roman military. He created professional standing armies and authorized the recruitment of landless peasants into the Roman army.

In the Final War of the Roman Republic, Octavian and Mark Antony fought against one another for sole control of the entire Roman territory. During the rule of the Second Triumvirate, Mark Antony had lived in Alexandria with the Egyptian ruler Cleopatra. The decisive battle of the Final War of the Roman Republic occurred in 31 BCE. The Battle of Actium was a naval engagement fought between the forces of Octavian and the forces of Mark Antony and Cleopatra. It ended in complete victory for Octavian. Shortly thereafter, Mark Antony and Cleopatra committed suicide, thus ending the war and bringing to a close the history of the Roman Republic.

The Tarquin Monarchy ruled the city of Rome in the waning years of the Roman Kingdom. The rulers of the Tarquin Monarchy were in power before the rise of the Roman Republic in 507 BCE. Also, due to their great antiquity, they are somewhat legendary figures whose lives cannot be reliably confirmed.

The Battle of Gergovia was fought in 52 BCE between the Gallic forces of Vercingetorix and the forces of the Roman Republic led by Julius Caesar. It ended in victory for the Gauls and forced the temporary withdrawal of the Roman army.

The Roman province of Gaul, conquered by Julius Caesar in 50 BCE, included significant amounts of territory in modern-day France and Belgium.

The Marian Reforms, enacted by Gaius Marius in 107 BCE, created a professional standing army drawn from the lowest ranks of Roman society. This meant that landless peasants could join the army for the first time in Roman history, and significantly, were paid a guaranteed wage for their service. The promise of significant wealth caused the common people of Rome to enlist in dramatic numbers and ensured that armies would be loyal to their generals, rather than to the Republic. This situation contributed to the decline of the Roman Republic by allowing some generals to grow immensely powerful (notable examples include Julius Caesar, Pompey the Great, Lucius Sulla, Marcus Crassus, Octavian, Mark Antony, and Marcus Lepidus).

The Battle of the Colline Gate was fought in 82 BCE between Sulla and the Marian forces loyal to Gaius Marius. It was the final battle of the brutal civil war between Sulla and Gaius Marius and ended with Sulla taking control of the city of Rome and Marius committing suicide.

Legionaries were trained soldiers in the Roman army. After the Marian Reforms, the Roman Republic possessed a professional standing army. This army was comprised of legions (a group of six-thousand soldiers) which was subdivided into cohorts and then again into centuries.

The Marian Reforms were a series of reforms to the Roman military enacted by Gaius Marius in 107 BCE. Prior to the enactment of the Marian Reforms, only relatively wealthy people could afford to serve in the armies of the Roman Republic. The Marian Reforms opened military service to the common people of Rome and, in doing so, dramatically altered Roman society.