Antoninus's Time Bombs

Antoninus inherited Hadrian's long list of client kings and auxiliary tribes. But he was hesitant to add new members to the roles. This worked fine during his own reign, but eventually jealousy from those on the outs led to an explosion of violence in the north. Marcus Aurelius' failure to nip the problem in the bud with more vigorous action is seen as one of the time bombs he unnecessarily handed off to his successors.