Short answers, pulled from the story.
The Battle of Philippi in 42 BC was the final engagement of the Liberators' civil war in Rome. The forces of the Second Triumvirate, led by Mark Antony and Octavian, fought against Brutus and Cassius, the leaders of Julius Caesar's assassination. The declared cause was to avenge Caesar's death; the underlying conflict was a long-running struggle between the Optimates and Populares factions of Roman politics.
The Battle of Philippi took place in October of 42 BC near the ancient city of Philippi in Macedonia, along the Via Egnatia. It consisted of two separate engagements: the first on the 3rd of October and the second, decisive battle on the 23rd of October. The armies fought on the plain west of the city.
The Battle of Philippi was fought between two sets of commanders. Mark Antony and Octavian led the forces of the Second Triumvirate, with Antony facing Cassius in the south and Octavian facing Brutus in the north. Brutus and Cassius commanded the Liberators, the faction that had assassinated Julius Caesar in 44 BC.
Cassius died by suicide at the first battle of Philippi after receiving a false report that Brutus had also been defeated. The battlefield was vast and clouds of dust made it impossible to see what had happened on the opposite wing. Believing himself beaten, Cassius ordered his freedman Pindarus to kill him.
Brutus took his own life after the second battle on the 23rd of October, 42 BC. After his army was outflanked and routed, he escaped into the nearby hills with only the equivalent of four legions. Seeing that surrender and capture were inevitable, he chose death.
The Battle of Philippi ended the Liberators' civil war and secured the Second Triumvirate's control of the Roman world. Roughly 14,000 soldiers from the defeated army were enrolled into the triumvirs' forces, and the town of Philippi was refounded as the Roman colony Colonia Victrix Philippensium. The battle marked the highest point of Mark Antony's career as the most famous Roman general and the senior partner of the Second Triumvirate.