Shortly after negotiating what would turn out to be a temporary peace arrangement with Decebalus and the Dacians, Domitian's armies in Germania Superior at Mogontiacum (Mainz) rebelled. Under L. Antoninus Saturninus, two legions (XIV Gemina and XXI Rapax) revolted for reasons that are largely obscured and lost to history (thanks to the later destruction of Saturninus personal documents), but the assumption has long stood that it was merely a local military revolt and not a wide spread conspiracy against the emperor.
It's quite plausible that the officers involved were rebelling against Domitian's rather strict moral policies which led to speculation that perhaps Saturninus and other officers were homosexuals being victimized by these strict codes (Dio and Pliny). Regardless, the rebelling officers took care to arrange peaceful terms with the neighboring Chatti (among the tribes whom the legions were charged with monitoring, who also took full advantage by destroying several area fortifications) likely to prepare a march.
Whatever goal Saturninus had is completely unknown and there seems to have been little indication of a plan. Neighboring legions, including Domitian's own I Minerva stationed in nearby Bonna remained loyal, and Domitian prepared a Praetorian expedition to meet the threat. Along with future emperor Trajan, who arrived from Hispania with VII Gemina in support of the emperor, Domitian moved against the rebels. Prior to his arrival, however, Aulus Buccus Lappius the governor of Germania Inferior, beat him to the punch and put down the revolt before it seemingly even began. Domitian took care to reduce the amount of coinage that soldiers could deposit within camp treasuries (these funds were apparently used to finance the revolt) and the rebellious legions were transferred east. With the short-lived and localized rebellion quickly behind him, terms were quickly reached with the Chatti as the emperor's attention was needed back in Pannonia and Dacia.
By the summer of AD 89 Domitian moved backed to the Danube to counter the Suebi tribes, Quadi and Marcomanni. These tribes had refused to aid the Romans in their war against the Dacians and Domitian needed to settle the empire's northern border. Two embassies were sent to negotiate peaceful settlements, but neither was successful. Speculation was that the Germanics had already negotiated a deal with the Dacians so it fell upon Domitian to remedy that hasty settlement negotiated in their previous encounters. Dio suggests that Domitian lost at least one encounter with the Marcomanni further weakening his position and giving Decebalus that much more room for negotiation. By the end of AD 89, an agreement was eventually reached, granting client status to the Dacians while leaving Decebalus entirely intact, with the Germanic issue temporarily being settled in the process. While Domitian would return to Rome and celebrate a double triumph (his supposed victory over the Chatti and the Dacians) and be honored with the presentation of his famous equestrian statue, Decebalus would remain a persistent threat to the Roman frontier.
Just 3 years later, in AD 92, Domitian's true lack of success the first time forced a return to the region. The same Marcomanni and Quadi Suebi tribes had joined forces with Sarmatians and had taken to raiding Roman territory. These raids, an indication of an ever worsening border situation, resulted in the destruction of Legio XXI Rapax (which was never reconstituted) and forced a serious response. This 'Second Pannonian War' resulted in yet again another temporary cessation of hostilities. Following Decebalus making good on his treaty, by allowing the Romans to cross Dacia to attack the Sarmatian rear, the Sarmatians withdrew from Roman territory and Domitian returned home after an 8 month campaign. The emperor received an ovation for this 'victory' rather than an additional triumph (clearly indicating his own dissatisfaction with the end result), but the situation was far from settled. Additional forces were continually sent to the Danube region over the next 3 years and there were some indications that Domitian planned yet another expedition. Perhaps had Domitian truly demonstrated the military skill of his father and brother, as was his initial goal after coming to power, he may have helped permanently settle the Danube border. Instead the Dacians were left to be dealt with by Trajan just a few years later, and the Germanics by Marcus Aurelius nearly a full century after Domitian's rather non climactic expeditions.