Answer:
Byzantine emperor at that time was Marcian (392-457) and the pope was Pope Leo I. Some historians believe that Marcian had an isolationist policy and that he was just worried for the campaigns of the Eastern Roman Empire. Whilst Pope Leo I was struggling to keep the barbarians and the Hunes out of the Roman Western Empire.
The tradition says that Marcian ignored the request from the Western Empire to take part as he had succeeded on rejecting Attila from his own territory and he didn´t want to get involved in a new direct confrontation with the Hunes.
Explanation:
