How did constantinople respond to numerous invasion attempts before 1453?

Constantinople fought and defeated all invasion attempts made before 1453, but these constant fighting made Constantinople very weak internally. Later in the year 1453, the Ottoman Turks were able to capture Constantinople because it had already become weak.The city was also weakened by the constant infighting of the people belonging to the  religion of Christianity. They also neglected the Muslims of Jerusalem. So it can perfectly judged that there was not a single reason behind the falling of Constantinople, but there were several facrors that worked together resulting in the downfall of Constantinople.