What were the causes and results of the Roman civil war?
The Great Roman Civil War, also known as Caesar's Civil War, lasted from 49-45 BCE and involved conflicts between Caesar and his supporters (known as the Populares) and those who opposed him (known as Optimates or Boni). Caesar's opponents were supporters of Pompey.
The causes of the war included the Senate's fear of Caesar's increasing popularity and power. While Caesar ruled with Pompey and Marcus Licinius Crassus in the First Triumvirate, Caesar's military conquests in Gaul made him more powerful than Pompey and Crassus. More troublingly, Caesar went around the Senate to gain governorships of the territories he conquered. In addition, he invaded Britain without the Senate's permission, and his military victories made him popular with the people. The Senate, under the direction of Pompey, tried to force Caesar to give up control of the army. In 49 BC, his infamous crossing of the Rubicon started a civil war in Rome, as it was considered treasonous to enter Rome with a standing army.
After the war, during which Caesar's forces defeated their opponents, Caesar was made dictator for ten years and then for life. Fears about his growing power led in part to his assassination in 44 BC by Brutus and Cassius and allowed the ascension of Octavius (later Caesar Augustus) to the throne. Augustus became the first Roman emperor. Therefore, the result of the war was the eventual establishment of the position of Roman emperor.
Since the first answer talks about some of the causes, I will go into some of the results.
First, I will assume that you mean civil wars - - Marius vs. Sulla; Caesar vs. Pompey; Octavian/Agrippa vs. Antony/Cleopatra. If we go into greater detail, there were even more. One observation is that many of these civil wars happened during the end of the republic (even if they did not know it was the end of the republic). From this perspective, something had to be done to restore peace and stability. This paved the way for Octavian to come into power. One can even make an argument that it was these wars, in part, that made room for Octavian. That said, he ushered in the peace of Rome (pax romana). The people loved this peace and quite frankly needed it. The bloody civil wars ravaged the Roman people. A quick glance at Vergil's work show the ethos of civil war and the hope for peace.
Eventually, Octavian (later to be called Augustus) introduced a new form of government - the empire. After Augustus, there would be emperors. Also from a cultural point of view, Augustus' reign would produce some of the most important works in the Latin language - Vergil, Horace and Ovid, to name a few. However, it must also be stated that civil wars would continue. In 69 AD, there was no less than four rival emperors fighting it out.
It's probably important to first note that there were several civil wars throughout Roman history. This particular one is often referred to as Caesar's Civil War. Ceasar, Pompey and Crassus, all through different avenues, formed the first triumverute. When their terms expired, Pompey remained as the sole consul. In the ensuing time, Caesar became a very powerful and popular military leader; so powerful, that Pompey became nervous and ordered JC's army to be disbanded. Caesar said he would if Pompey broke up his own army. Pompey did not, which first led to important figures such as Marc Antony declaring loyalty to Caesar, and eventually led to Caesar crossing the Rubicon River and declaring war on Pompey. Caesar, of course, won this battle but was eventually assassinated by the conspirators. Long story made short, as a result of Caesar's defeat of Pompey and the chaos that ensued after his assassination, the Roman Republic started an extremely quick decline. This ended in Caesar's officially named heir, Octavious, being named the first emperor of Rome; thus, the end of the Republic and the beginning of the empire.