Final answer:
Belisarius used military force to conquer the Vandals, decisively defeating the Vandal army in North Africa and reclaiming the territory for the Byzantine Empire.
Step-by-step explanation:
The tactic Belisarius used to conquer the Vandals was military force. This is corroborated by historical accounts that detail how Belisarius was sent by Emperor Justinian to Vandal-controlled North Africa in 533 with a relatively small contingent of soldiers and cavalry. Despite the size of his force, Belisarius was able to defeat the Vandal army decisively and reclaim North Africa for the Byzantine Empire within a year. Following this victory, Justinian then deployed Belisarius and his forces to Italy to continue their conquests against the Ostrogoths, further highlighting the reliance on military prowess over other methods such as diplomacy, economic sanctions, or religious conversion. This strategic use of military capability under Belisario's command was a significant factor in the successful expansion and recovery of territories once lost by the Empire.