What made it difficult for the Byzantine empire to hold on to Justinian's coonquests?

Answer 1

Italy was lost eighteen years after the end of the war with the Ostrogoths with which the Byzantines took Italy. The war lasted 19 years. It left parts Italy devastated. Some areas in the north were depopulated. The Byzantines were exhausted and their resources were drained by the war. They were unable to respond to the invasion of Italy by the Lombards. The Visigoths retook southern Spain 26 years after it was taken by the Byzantines. The Byzantine Empire was severely affected by the Plague of Justinian, one of the worst epidemics in history, which killed millions of people. The gains in Africa were lost some 150 years later, in the late 7th century, when the empire lost its lands in Africa and most of its territories in Asia because of the Arab invasions.