How did constantinople respond to numerous invasion attempts before 1453?

Constantinople was able to fight back against the numerous invasion attempts before 1453, but with each fight it got weakened. This resulted in the fall of Constantinople in the year 1453, at the hands of Ottoman Turks. Constantinople was not only fighting against the Turks, but also against the fellow Christians. The Turks did not care about the Muslim population living in Constantinople. Constantinople never grew stronger with the resistance they put up against the several external aggressors. If that has been the case, then they would not have been defeated by the Ottoman Turks.