The Sullan period highlights the rift which was beginning to form between the concept of legion loyalty to Res Publica and loyalty to individuals. It also highlights one of the major problems of Roman late Republican politics: one needed to be successful in the military sphere to attain the sort of power at Rome beyond that which the Republican machinery of government allowed. But one also needed to be in the capital almost constantly to guard against the schemes of one's enemies in the senate. One episode in particular was a turning point:

In 88 BCE, while consul, Sulla had some problems with a pesky Tribune of the Plebs called Sulpicius. The tribune had enacted some legislation which Sulla attempted to block (with a "iustitium"). The result was one which was becoming more and more predictable: a riot. During the riot, Sulla was forced to flee for his life to the home of his political enemy, Marius. There the two worked out a deal in which Sulla would lift the iustitium in exchange for safe passage out of the city, where he could join his army (which was still besieging a Campanian town called Nola which hadn't got the memo that the great Italian Social War had ended). As soon as he (one of the rightful consuls for that year) was out of the city, Sulpicius and other anti-Sullans took steps to alter the agreed-upon distribution of commanders for an upcoming campaign against Rome's big enemy in the East, Mithridates. The command (and the prestige attached) had been Sulla's, but now it was transferred to Marius. Marius sent out legati (right-hand men) to take control of the army at Nola, which was technically legal under the new anti-Sullan dispensations. Sulla's soldiers, when informed that they were now Marius' soldiers, (apparently) killed the Marian legati and gave Sulla their support anyway (under Sulla, they had won great victories in the Social War and Sulla had won Rome's highest military honor, the corona graminea or "grass crown.") Sulla then marched on Rome, technically still a Roman consul but followed by an army which was now, technically, not his to command any longer [it is complicated because he still ostensibly retained imperium as consul, if not mandate].

He took the city, arranged for all his political enemies (including Marius) to be declared enemies of the state, and then with them out of the way compelled the rest of the government (cowed by Sullan troops in the capital) to pass a series of sweeping reform bills, the content of which are not clear to we historians (our source is Appian, and he is not always the greatest source to have). The power of Tribunes was reduced in some way; changes were made to the way the comitia centuriata worked (an assembly of the people); and there was some financial legislation. This was late in the year 88. In early 87, as had been previously agreed, he left Italy with his army to confront Mithridates in the East.

This was not the famous, bloody Sullan dictatorship, however. That would come later. But this initial move set the stage for the later dictatorship.