Almost immediately upon the death of Augustus, and his subsequent deification into the Roman Imperial cult, the legions in Pannonia and Germania began to revolt. The legions that guarded the Rhine and Danube rivers, by the far the largest concentration of military might in the western world, were unhappy with the terms and conditions of their service. In direct relation to the transfer of imperial power, the loyalty of the legions, who swore an oath directly to Augustus not the state or 'office' of Emperor, was severely tested.
In Pannonia, the revolt was really a continuation of the disorder that Tiberius has put down while Augustus was still emperor. When the men demanded more pay, fewer years' service, and other 'retirement benefits', Tiberius' son Drusus wisely managed to delay the mutiny. Convincing them that he didn't have the authority to deal with such matters, an embassy was sent to Rome on their behalf, which quelled open mutiny in the interim. A lunar eclipse (a sign of disfavor from the gods) and terrible stormy weather helped further dampen the troop's zeal. Drusus followed up with extreme authority, hunting down the ring leaders and putting an end to a volatile and potentially very dangerous situation.
In lower Germania, where Tiberius' adoptive son and heir Germanicus was in place, the legions revolted for similar reasons but were also affected by Germanicus' very presence. Extremely popular with the men, perhaps for his direct familial relationship with Augustus, or just because of a lack of affinity with their former commander, Tiberius, some mutineers even suggested that Germanicus replace Tiberius as emperor. Germanicus was in a very delicate situation, trapped between Tiberius and an army disloyal to the empire, but pledging loyalty directly to him. Given the circumstances, it's not surprising that the situation was poorly handled. Germanicus even offered to commit suicide rather than be disloyal to Rome, an offer which was seemingly accepted by the men. It proved his loyalty to Tiberius, but the tactic failed to produce order, and he next forged documents indicating that Tiberius had accepted all their demands. This ultimately backfired, as the truth came out, and did little to help, but actually hindered another potentially disastrous situation. Finally, order came simply by discrediting the soldier's sense of honor and dignity. Germanicus ordered his wife, Agrippina (direct granddaughter of Augustus) and their son Gaius, or Caligula (little boots), who was so named by the troops in love and deference to the miniature legionary costume he wore, to leave the camp fearing for the safety. The men responded with seemingly true remorse and begged for the return of Agrippina and their little mascot. Germanicus refused until they took it upon themselves to restore order. With that ultimatum, a veritable purging of the mutiny leaders occurred and the Germanic legions pledged loyalty to Tiberius.
Germanicus wasn't a fool, however, and was well aware that idleness may have been the true cause of discontent. For the next several years (14 - 16 AD), he led a number of punitive campaigns against the Germanic tribes across the Rhine. While these did eventually restore at least one lost standard from the Varus disaster of 9 AD, the campaigns were actually far more dangerous to Roman security than those that had occurred before. Sticking to Augustus' policy of border maintenance rather than expansion, Tiberius all but ordered Germanicus return to Rome in the guise of a triumph, celebrated in 17 AD. This was significant in that it not only marked the end of open aggression against the Germanics until the reign of Marcus Aurelius some 150 years later, but it was also the last non emperor general to celebrate a triumph in Roman history.
Having celebrated that triumph, Germanicus now in his early 30's, was clearly defined as Tiberius heir per Augustus's wishes even above Tiberius's own natural son Drusus. In 18 AD, he was sent east with 'Imperium Maius' in much the same manner that Agrippa had been under Augustus. Essentially Germanicus was acting as a second imperial authority in the east. However, difficulty with Cn. Calpurnius Piso, governor of Syria began to unravel the stability of the still young principate. Germanicus fell ill and died just a year later, 19 AD, accusing Piso of poisoning him in the process. Piso was eventually brought to Rome and put on trial for treason, one of the earliest of many such trials during Tiberius' reign, committing suicide when it appeared that he held no hope. Tacitus, writing a remarkable account in his 'Annals' claimed that Tiberius may have had a hand in the affair, citing jealousy and fear over Germanicus' popularity with the people and the legions.
Whatever the truth, Germanicus was dead and Tiberius elevated his natural son, Drusus to the role of heir. However, a split occurred between Germanicus' remaining family, the one branch that held direct connection to Augustus, and this would strain imperial politics for the remainder of Tiberius' rule. This split would also allow the rise of a man who would take this strain to new heights, not just within the imperial family but between all facets of Roman society. This man, L. Aelius Sejanus, the Praetorian Prefect and soon to be emperor in all but official title, would be the first to make the imperial body guard a political force of their own, and pave the way for Praetorian influence for centuries to come.