How did the struggle against external danger influence the development of Byzantium?

This refers to the period from the 6th century to the middle of the 15th century.
From the end of the 6th century, Byzantium constantly waged wars along the perimeter of its borders. The opponents were: Arabs, Slavs in the Balkans and in the Crimea (Vladimir’s campaign against Kherson in 988), Seljuk Turks from 1071 and Ottoman Turks from 1300, as well as crusaders from 1204.
As a result, Byzantium weakened in the XIII century and the leading role in Europe began to move to small trading states of Southern Europe, for example, Genoa and Venice. In 1402, the Turks almost took Constantinople, but Tamerlane’s campaign against Ankara extended the existence of Byzantium for 50 years.