Rome's mercenary shortcut weakened political control of its armies

A comparison with Song military burdens turns to the Roman problem of who supplies military manpower. Emperors found non-citizen casualties easier to defend politically and assumed mercenary commanders posed less danger to the succession. Cash alone, however, could tie soldiers to the general who paid them rather than to the state, giving a successful commander leverage to challenge the government. An effective army needs institutional and political loyalties beyond salary, because combat skill without attachment to the wider state can endanger the system it serves.