How did Galba lose power according to Tacitus’s Histories?

According to the Histories by the Roman historian Tacitus, the emperor Galba lost power due to a combination of unpopular administrative decisions and the shifting loyalties of the military and political elite.

Galba’s downfall was precipitated by several key factors:

• Financial and Military Policies: His attempts to curb Nero’s extravagant spending and his refusal to pay the Praetorian Guard their promised donative alienated his supporters.
• Provincial Unrest: By rewarding the regions of Gaul that had supported the rebellion against Nero, he outraged the legions of Upper Germany, who had defeated that rebellion. These legions subsequently refused to swear allegiance to him and proclaimed Vitellius emperor.
• Succession Crisis: In an attempt to secure senatorial support, Galba chose Lucius Calpurnius Piso Frugi Licinianus as his heir, bypassing his former ally Otho. In response, Otho secured the support of the Praetorians with promises of payment.

Ultimately, the Praetorian Guard murdered Galba and Piso in the Roman Forum on January 15, 69 CE. Tacitus famously summarized Galba’s reign with the epigram: "He would have been capable of ruling, except that he ruled."