In order to make up of the loss in manpower as a result of the continuous wars of the second century, Marius did away with the minimal requirements of the soldiers—now men without means and property could join and he enrolled a large volunteer army from the proletariat. In addition, he made practical changes in organisation of the army and weaponry.
Marius took with him a quaestor to Africa, Lucius Cornelius Sulla. The war continued for another two years until Jugurtha was betrayed by his relative  to Sulla, thus ending the war. Marius, as commanding general, received the credit but Sulla had been largely responsible for the victory through diplomacy and guile. This would eventually become a point of contention between the two of them, but for now, Marius kept Sulla, as his subordinate in the campaigns against German tribes ; later, Sulla transferred to Marius’ consular colleague, Catulus.
The war with the German tribes arose because two tribes, the Cimbri and Teutones, in search of new homes moved into first southern France and then northern Italy. A series of consular commanders between 113 and 105 BCE was unable to halt the Germans, and now Rome's borders were open to the invaders. Based on his past record, Marius was chosen to save Rome. In spite of the law that laid down intervals between tenures of the same office (lex annalis), Marius was elected as consul for 104 BCE onwards until 100 BCE to deal with the invaders. He led the Roman armies, and in two significant battles (Aix-en-Provence in 102 BCE and Vercellae in 101 BCE) defeated the invading armies so thoroughly that it would be two generations before they again seriously troubled Rome. For that, Marius was called the third founder of Rome . Sulla's contribution in the victory was also important. Among other things, Sulla captured a chieftain of the German tribes, persuaded another tribe to become allies of Rome, and led Catulus’ army in the Battle of Vercellae . Although Catulus, not Sulla, celebrated the triumph since Sulla was under the command of Catulus, ‘Sulla, at least, must have known that whoever said "Catulus" really said "Sulla." … So Catulus, that lazy versifier and art-collector, acquired one treasure that must have been the last he ever expected to collect—a Triumphal Car. It ought by rights to have been inscribed: "A present from Lucius Cornelius Sulla."’ 
continue to Marius and Sulla: Conflict
*I am only giving context to the Apollonian propaganda of the Marian and Sullan factions, and as a result, may not pay much attention to important events and may concentrate on unimportant events. I am not analysing the civil wars, the fall of the Republic, the outcome of Marius’ army reforms, assigning blame, second-guessing the motives of the people, etc.
When I say the Marian faction, I am including the adherents of Cinna and Carbo. Also, I am using the word “faction” loosely. The Romans did not have political parties in the modern sense. The Roman substitute for party is amicitia (friendship) .
I would like to thank Robert W.M. Greaves of Ancient Biographies for proof-reading these articles.