What were the factors that led to the fall of the Islamic Caliphate, and what are the conditions that could lead to its return?

Several reasons led to the weakening of Muslims and the fall of the Caliphate, including: their turning away from the teachings of their religion and the disunity of their word, abandoning work, production, and jihad, their inclination towards worldly life, and their ignorance, while the enemies of Islam became active and exploited their weakness. For the return of the Caliphate, there must be a sincere return to the Book of Allah and the Sunnah (definition) of His Messenger, following the prophetic methodology in building the individual and society, and getting rid of the causes of weakness, through individuals adhering to the religion, uniting, and forsaking discord.