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.
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