The reasons for the eventual fall of the Abbassid Caliphate which occurred in 1100-1258 CE are the following.
1) Corruption: The Abbassid Caliphate had become one of the richest and most prosperous states in the world at that time, changing its leadership from honest brokers of power (Amir al-Mu'aminin - Prince of the Believers used to actually mean something) to individuals more concerned with money. This created strong resentment from those who were outside of the Abbassid purview.
2) Mawali Inclusion: The Abbassids were an Arab Caliphate (as opposed to the Samanids who were a Persian Caliphate) and were expected by many Arabs to treat other Arabs better than the Mawali (Non-Arab Muslims). However, the Abbassids consistently treated Persians equal to or better than their Arab brethren which created animosity and a sense of betrayal. Many Arabs saw the Persians as the major backers of the Caliphate and that they were a tool for Persian interests. It was also perceived that the Persians were first servants to the caliphs but climbed way up the social ladder to a place they did not belong.
3) Turkish Armies: Armies like the Mamluk (who were retained by the Abbassids for the defense of the Caliphate) were Turks who defended an Arab State. Beginning in this period, they began to realize that they had the capacity to create their own states considering how vast their powers were as a military. This idea also came to the fore for Turks outside of the Caliphate. As a result, there were Mamluk uprisings, Seljuq attacks, and other Turkish Armies turning against Baghdad.
4) Rise of the Mongols: Hulegu Khan put the final nail in the coffin by massacring Baghdad and a number of Persian cities when he conquered the territory for the Great Khanate.
Some other Muslim groups rebelled against Abbasid rule, causing them to lose control of the empire.
The Abbasids took control
The abbasids were rulers of the Islamic Empire back in the 700s to 1200s.
The Abbasids, as the ones from the Islamic Empire.
a group called Abbasid gained support from other Muslims and when the abbasids invited the umayyads over for dinner and a meeting the abbasids left the room leaving the umayyads to be assassinated
the abbasids dies
The First true Islamic Empire was established by the Second Rightful Caliph Hazrat Umar RAU. It was followed by Ummayyad Family and then Abbasids.
Baghdad.
The Abbasids moved their capital to Baghdad because they wanted to move it closer to Damascus during the time when Umayyad's capital was Damascus. In which means that the Abbasid empire wants to overthrow the Umayyad empire.
shiites were under control and any political action was banned for them and Imam of shia Muslims was in prison by abbasids.
they expand too much and lose control of everything
through a strong bureaucracyby Dictatorship. they killed and Jailed Imams of Shia Muslims.
During the last Abbasids the central was weak and the strong dynasty was emerged by Seljuk who took the hold of central government, the whole military was control by them. they decided the administrative affairs and the Abbasids rule by name and they were decline.