Although the other choices are quite true somehow, Constantine’s decision to stop persecution of the Christians was the most significant. Because of his conversion, he stopped Christian persecutions immediately. This led to and became the turning point of Christianity. Due to his conversion, he was able to legalized Christian worship in a form of a decree which we call the Edict of Milan. Constantine became a faithful follower of Christianity and was considered an influential individual in Christianity.
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.
