However, after 1 1 century, the Italian city-state gradually replaced Byzantine's dominant position in Mediterranean maritime trade, which led to the decline of Byzantine maritime transportation and the inability of Byzantine navy to recruit experienced maritime personnel from its own country to enrich the navy. In this way, the strength of the Byzantine navy can not be guaranteed, and the Byzantine maritime caravan can not be effectively protected by its own navy, which leads to the decline of commerce, forming a vicious circle and eventually leading to the complete collapse of the Byzantine navy.
2. Lack of martial spirit, the core part of the Byzantine Empire (around the Aegean Sea) has always attached importance to commerce, hated soldiers, and was not enthusiastic about joining the army, which led to the Byzantine Empire recruiting soldiers only from the border areas with simple folk customs such as Asia Minor and Danube; But later, due to the silkworm swallowing whale food of Frankish Empire, Arabian Empire and Ottoman Turkey, after all these areas were lost, Byzantium could not find a suitable and sufficient source of soldiers, and its army declined accordingly.
3. The development of Western Europe and the Middle East, the Byzantine Empire in the early Middle Ages, because it inherited the greatest legacy of the Roman Empire, was much higher in science and technology, culture and economy than neighboring countries, and its comprehensive national strength was extremely high, so that Byzantium had great advantages over other countries in system and technology (such as Byzantine heavy cavalry, Greek fire and Byzantine military region system). However, with the development of science and technology, Byzantine technology was relatively backward and was finally destroyed by Turkish artillery.