Why did Diocletian’s tetrarchy fail to prevent struggles for imperial power?

Diocletian’s tetrarchy failed to prevent struggles for imperial power primarily because it lacked a mechanism to ensure a legitimate and stable succession, ultimately clashing with the deeply ingrained hereditary principle.1

While Diocletian intended for the two senior Augusti to abdicate after 20 years and be succeeded by their respective Caesars, this system relied on the voluntary cooperation of the rulers and ignored the strong attachment that both the military and the general population felt toward hereditary succession. When Diocletian and Maximian abdicated in 305 CE, the system quickly collapsed as the sons of former emperors—such as Constantine and Maxentius—were proclaimed emperors by their respective armies, disregarding the tetrarchic rules.12

Furthermore, the tetrarchy was a transitory arrangement held together largely by Diocletian’s personal authority and statesmanship. Once he retired, the lack of a universally accepted method for transferring power led to a period of intense rivalry, civil war, and successive eliminations among the various claimants to the title of Augustus.12