The painting shown is depicting the fall of the Byzantine Empire by war, and by the fall of its capital, Constantinople. In this painting we can see the walls of Constantinople being defended by the Byzantine forces, but the Ottomans manage to over come them by both land and sea. The Ottomans are getting up the defense walls and get into Constantinople, largely outnumbering the defense forces, and capture the city. The fall of Constantinople marks the end of the great Byzantine Empire that lasted a whole millennium more then its western counterpart, the Roman Empire.
Because is depicted the invasion of Constantinople (the Capital of the Byzantine Empire) with the enemy army, in this case, the Otomans, climbing the walls while the Byzantine soldiers attempt to protect the city.
Explanation:
By the mid-fifteenth century, the Byzantine Empire had been in decline for a long time but remained an important bastion of Christian Europe facing Muslim Asia. The Ottoman Turks, in their turn, met resistance only in Constantinople. To them, the city had enormous prestige, both as a center of Christian faith as a symbol of imperial power. Its fall had repercussions throughout Christendom and marked the end of the European Middle Ages.