From the beginning of the 2nd century BC, power was contested between two groups of aristocrats: the optimates, representing the conservative part of the Senate, and the populares, which relied on the help of the plebs (urban lower class) to gain power. In the same period, the bankruptcy of the small farmers and the establishment of large slave estates caused large-scale migration to the city. The continuous warfare led to the establishment of a professional army, which turned out to be more loyal to its generals than to the republic. Because of this, in the second half of the second century and during the first century BC there were conflicts both abroad and internally: after the failed attempt of social reform of the populares Tiberius and Gaius Gracchus, and the war against Jugurtha, there was a first civil war between Gaius Marius and Sulla. A major slave revolt under Spartacus followed, and then the establishment of the first Triumvirate with Caesar, Pompey and Crassus.