It is strange that in the wake of War With/Against Iraq that Americans and Westerners haven't attempted to learn 'more' about Islamic history. It is quite fascinating. Tales of heroism interpersed with treachery & deceit jumbled up with bravery & tenacity. But yes books & sources are scace.
That said The Caliphate declined because it was a system dependent on a strong gifted leader. It was an imperfectly ad-hoc agreement between people whose only common link was their religion and when those people began having arguments over religion things got worse.
One of the chief reasons for the decline was the very dynacism of Islam. Yes the religion conquered a diverse number of 'nations' but in time those nations asserted their Independence and broke away. And by growing wealthy & powerful the Caliphate became the target of agressive groups such as The Mongols who wanted to seize their riches and without strong leaders war is a futile exercise. The Calipjate was eventually undone by the wars it generated, the conflct they had sown...
As my income testifies I am no scholar so will throw some links & words your way.
http://www.wsu.edu/~dee/ISLAM/UMAY.HTM
""" When Muhammad died in 632, he left a political organization that was entirely centered around him. He was a political and military leader and he was the source of revelation. When political or social difficulties came up, not only would they center on Muhammad, but sometimes through revelation be mediated by Allah himself.
The central role of Muhammad left the growing Islamic polity with several difficulties. The first was the status of revelation itself—this became settled with the establishment of the definitive Qur'an . A more serious problem, though, involved the political and military succession to Muhammad. The only working model was an individual leader, but that leader had the authority of God behind him.
No-one seems to have thought very much about the succession to Muhammad before his death. No-one regarded Muhammad as divine or immortal, but no-one really considered what would happen after his death. The solution was cobbled together by the most powerful followers of Muhammad. There was disagreement—in fact, violent disagreement—between the Meccan followers of Muhammad who had emigrated with him in 622 (the Muhajirun, or "Emigrants") and the Medinans who had become followers (the Ansar, or "Helpers"). In the end, however, Muhammad's father-in-law, Abu Bakr, was named the khalifa or "Successor" of Muhammad. A new religion and a new circumstance had formed a new, untried political formation: the caliphate.
The Patriarchal Caliphs The earliest caliphs were relatives and followers of Muhammad himself. Under these four caliphs, the political, social, and religious institutions of Islam would be solidified, including the definitive edition of the Qur'an . The world of Islam would expand far beyond the borders of the Arabian peninsula during their tenure—east into the Persian empire, north into Byzantine territory, and west across the face of northern Africa.
Because of their foundational status and the fact that they were direct followers of Muhammad, these first four caliphs are called the patriarchs or patriarchal caliphs of Islam. For many Muslims, this was the golden age of Islamic government when a true Islamic polity was in existence; from some Muslims, such as Shi'ite Muslims, this was the only period when there was legitimate Islamic government. In this view, the founding of the Umayyad dynasty ushered in more than a millenium of illegitmate government. """
http://www.answering-islam.org/Books/Muir/Caliphate/index.htm
""Musta'sim last Caliph, 640-656 A.H. 1242-1258 A.D.
IN the year 640 A.H. Al-Musta'sim became Caliph, — name vainly meaning He that maketh the Lord his refuge; — a weak and miserly creature, in whose improvident hands the Caliphate, even in quieter times, would have fared ill. Between the Chief Secretary, an ambitious and unprincipled courtier and the Wazir Ibn al-Alkami bitter enmity prevailed. The Wazir, strange to say, was a Shi'ite; as such he is of course denounced by orthodox annalists, who even accuse him of seeking relief for his persecuted fellow-sectaries by treacherous communication with the Mongols. Others assign him a more patriotic rôle; and, indeed, we need not to travel beyond the imbecility of the Caliph and the demoralisation of his now shrunken kingdom, for the causes of impending ruin.
His character.
Of Al-Musta'sim himself there is little to relate. As characteristic of his meanness, we are told that he appropriated the state jewels of the Chief of Kerak, who with difficulty obtained their partial restitution by proclaiming the Caliph's dishonesty before the assembled pilgrinis at Mecca. His influence was felt, however, somewhat in Egypt. The 'Abbasid cause being now recognised there, the Sultan sought and obtained at Al-Musta'sim's hands recognition of his title and the insignia of investiture. The Caliph also repeatedly interposed to mediate between the Ruler of Damascus and the Sultan of Egypt.1 It was for his interest to help towards the establishment of a
1 When appealed to by the two rival claimants, he sent one of them a knife with jasmin decorations as proof of his good will, but the robes of installation he declined to send till afterwards. He was opposed
Hulagu's designs on the West, 653 A.H. 1255 A.D.
Meanwhile, as a tiger watching its prey, the Mongol was preparing from afar for the fatal irruption on the fair provinces of the West. Al-Musta'sim had been now thirteen years on the throne when Hulagu proclaimed a campaign against the Ismailians, and invited all to join in crushing the hateful race. The call met with no response from the Caliph. In the following year, the overthrow of the Ismailian power left the Conqueror free for his designs on the farther West. The state of Bagdad may he surmised at this time from its being the theatre of unceasing strife between the two hostile ministers already named, who accused each the other of treason. The Secretary went so far as even to rise against the Caliph himself, and, with the mob at his back, force his hand not only to declare him blameless, but to have his name recited in the public prayers.
His advance on Bagdad, 655 A.H. 1257 A.D.
Just then, Halagu, who was resting at Hamadan, sent a threatening embassy to Bagdad. First, he upbraided Al-Musta'sim for having failed to aid in the campaign against the Ismailians, as the enemies of mankind. Now, therefore, he bade him to raze the defences of Bagdad and commanded that, to learn his will, he must forthwith repair in person to his Court, or else send his Wazir and chief officers for the purpose; — which done, he was ready to leave Al-Musta'sim in secure possession of what he had. The foolish Caliph in reply descanted on the multitudes ready to hasten for the defence of the Vicegerent of the Prophet; and while declining to dismantle the city, sent an Envoy with presents and an otherwise soft reply. An immediate advance was the sole response of Hulagu.
City seized and sacked, 656 A.H. 1258 A.D.
The helpless Caliph, persuaded by his Wazir, had already marshalled an embassy of submission, when the Secretary and excited populace forced him instead to send a letter of defiance to the Conqueror, reminding him of
the Saffarids' fate, and of others who had dared attack the "City of peace." The warning was not without effect upon the superstitious Mongol, whose fears were now excited, and now quelled, by his astrologers. At last, satisfied of the safety of the enterprise, he made his Tartar hordes, from every side, converge upon the fated city. There the weakling at one moment wildly sought to gather troops for its defence; at another sent offers of a yearly tribute to his enemy. Ever and anon he looked for some ready fortune, such as had saved in like case his predecessors, and expected even the hand of heaven to interpose.
i. 656 A.H. Jan., 1258 A.D.
In the first month of 656 A.H. the Mongols routed a column which held Al-Anbar, and pursued the few survivors to the western quarter of the city. Shortly after, Hulagu himself, marching down the eastern bank, attacked the opposite quarter. In vain the Caliph sent his sons to plead for mercy: in vain he deputed the Wasir to seek for terms. All that could be wrung from the conqueror was safety for the chief inhabitants. Hulagu had already stormed part of the city when he sent for the Commander-in-chief of the Caliph and his Secretary to arrange for the cessation of hostilities.
4th ii. A.H. Feb. 10
They went, but notwithstanding promise of safe-conduct, were put to death, with all their followers. Nothing remained for Al-Musta'sim but to go forth himself, which he did at the beginning of the second month, followed by his sons and the leading citizens. They were received with outward courtesy. The Caliph and his sons were remanded to a tent; and the inhabitants warned to quit the city, which would then be given up to plunder. The wretched Caliph, following in the tyrant's suite, was forced to witness the sacking of his palace, and there point out his hidden treasures with golden ingots of untold weight. After many days of rapine and conflagration, Hulagu put an end to the pillage, and took the city for his own.
Last of the Caliphs put to death, 14th ii. 656 A.H. Feb. 20, 1258 A.D.
Al-Musta'sim, now in the Mongol's way, was put to death in the middle of the second month, 656 A.H., with all the members of the house on whom hands could be laid. And so, suffering a fate similar to that which five centuries before it had itself inflicted on the Umeiyads, the 'Abbasid dynasty came to a violent and untimely end. ""
Peace,,,,