How did the conflict between Marius and Sulla happen?
The conflict between Sulla and Marius was largely a struggle for power between the two individuals over who should control Rome. At the time, an eastern king called Mithridates had taken over a large area of Roman territory in Asia Minor and was threatening Rome’s influence in Greece. In order to combat this, the senate voted to send an army over to defeat Mithridates.
The senate voted for Sulla, a young and ambitious general who had proved himself in the Social War, to lead the army. Marius, who had held considerable power in Rome but was slowly losing favor due to his age and hunger for power, was furious at this decision as he felt he deserved the glory of leading the armies. A conflict ensued within the Roman Forum due to this decision, which eventually turned into an all out brawl where a number of officials and citizens were killed, including Sulla’s son-in-law. Sulla then fled the city and went to the camp of the legionaries who he had led in the Social War.
He told them of what had happened and when an official arrived declaring that Sulla would be deposed and Marius would seize control of the armies the official was executed and Sulla marched on Rome. This was an unprecedented event, as no general had ever marched against Rome before. Upon arriving in the capital, Sulla declared himself dictator and sent out an order of execution against Marius and his supporters.
In all, the conflict arose due to both individuals struggling to control Rome and for the glory of conquest.