Contrary to opinions in previous posts, the Buyyids are on a steep decline long before the Saljuqs, at least approximately 60 years prior to Tughlaq al-Saljuq captures Baghdad from the Buyyid-Abbasid state. The Buyyids were the characterization of a peculiar trend in the end of the First Abbasid period, whereby the Abbasid Caliphs while titularly the legitimate rulers, were tied as separate arms to another state. This in essence, the Buyyids were the same state as the Abbasid, in a sort of what could be called dual rule. This infact, was the position the Buyyids took in its rule, that of the Shah ensuring power on the ground (in theory) and the Caliph remaining the religious power and ruler of Baghdad, the only true city in the empire at the time. So it can be said clearly, that Buyyid power was tied inexorably to the power held by the Abbasid and the acceptance of Caliphate authority in the Islamic world. Unfortunately for the Buyyids, this is nearly non existent in the 900s, especially considering the subversion on the part of the Abbasids against the Buyyid Shahs following the reign of Adud al-Dawla. This subversion is mostly seen in the Abbasid's enthusiasm in supporting Mahmud Ghazni and the fanatical processions given to the Turkish Muhjahadeen under the service of the Ghazna who invaded Hindustan. Enthusiasm such as this, was an extreme detriment to the power and legitimacy of the Buyyids both as the sword of Islam and as the sole protector of the Abbasid throne.
Ghaznavids then pushed further into Buyyid power in the east of Khursan. Buyyids however, could not truly take the war to the Ghaznavids due to its extreme precarious position. This position was characterized by a rebellious client in Baghdad, who possessed with a single sentence, the ability to fracture the empire; the ever present Fatimid menace with its strings attached all across the Islamic world via Da'i (Shi'i revolutionary preachers, similar to say communist revolutionaries,,, I often compare the Fatimid foreign policy to the Soviet Comintern pre Stalin); the series of criminal syndicates, pirates and bandits ruling vast parts of southern Iraq; and finally, the Byzantine apparent ascendancy in the region (or Apogee as Norwich says).
All of these factors contributed to a special inaction until a point of no return was reach for the Buyyid. The Buyyid state thus, with all its great potential, was essentially doomed.
Each factor though, produces an interesting discussion however.
While the Abbasid had power to greatly disrupt the Buyyid overlords, that does not mean actual power was held. Abbasid power in the mid to late 900s was purely that of power in courts, subversion, intrigue and formalities. They dictated the flow of formal courts in Baghdad and remained renowned for the skills of their finest web weavers. As well, Abbasid power with its religious authority and intrigue, also found power in the nearby House of Wisdom, amongst zealous intelligentsia who favored a pure Abbasid power in the region and rejected the perceived excess of foreign rule. However, the Abbasids other than these, had no way to mobilize outside Baghdad and if free, could only launch small expeditions outside the walled city of Baghdad to tame nearby suburbs. Thus, regardless of scenario, the only option with a fall of Buyyid power is further decentralization (already at an extreme height) or Abbasids seek protection.
In the event of the inevitable Buyyid collapse, who would the Abbasids seek aid from? Especially considering the defeat of the Saljuqs by the Ghazna, they have few candidates. The obvious immediately is the Ghazna. Abbasid powers could request aid from the Ghazna, perhaps offering the seat of Sultan in Fars in exchange for protection? This would leave either lesser clans or Mamluks in control of Wazirastan as a vassal. This however calls into question the willingness of the Ghazna. Their response is unknown to me, it could go either way. On one hand, how could they reject becoming not only the greatest muhjahid state on earth and now the Mace of Allah and Defender of the Faith? Yet, they also wound know what they were walking into, a world different from the land of honest warfare and dominance in the edges of Islam, to the heart of subversion (as the Saljuqs wound come to woe, woeful is Empire for the true warrior as it is said) and further, they would enter conflict with the Fatimids (who the Ghazna have experience with through the Da'i subversion of Islam in the Indus Valley).
Another unexpected response I can see... Most interestingly, many of the intelligentsia of the Mu'Tazilah of the X century Baghdad, had favor in a particular Empire... This was leanings of the Abbasid to possibly favor the Byzantine Empire of the East against the Shi'i Fatimids, in a short term agreement. Such an agreement was always a wish of the Islamic powers following the Qarmatian period of terror, since Byzantium while an eternal enemy, was to Mu'Tazilah and Sunni of Baghdad of all views, preferable to the Shi'i who was worse than anything a Christian could hope for. This wound essentially consist of a offer of peace with Byzantium and a secret offer of alliance that wound ensure the protection of Iraq from the Fatimids. Byzantium would not be able to resist this offer in any way. Mind you, a Saljuq-Byzantine alliance was very possible in the same time frame; the only thing in the way, was the pride of Byzantium and their choked bureaucracy. Mind you, the reason for intellectuals having a positive opinion of Byzantium, was this period of Islam's fetish for Greek and Roman ways of life.
Inside Baghdad, population is large, the second or third largest city in the western world (behind Constantinople and possibly Alexandria). The population of the city consisted of over 200k humans and thousands of draft animals. Slaves, merchants, intellectuals, nomad warriors (swords for hire), Bedouin, craftsmen, criminals, etc all were seen in the mosaic of Abbasid period Baghdad. The diverse city was filled with every religion too, Sunni comprised the majority, Syriac speaking Christians made up areas of the civil service (especially scribes for higher up Muslim scholars), affluent Jewish communities, Turks, Persians, Mu'Tazilah intellectuals and magistrates etc... Thr only group rejected, was Shi'i, who remained extremely ostracized and the fearsome Khawarij cliques who lived in silence. Both were seen as sources of revolution and dissent in the Abode of Islam, especially the Shi'i who were seen as the allies of Qarmatiand and spies of the Fatimid menace. Shi'i infact, were not uncommonly lynched and attacked publicly and killed for their faith if found. Thus, thousands and probably millions of Shi'i lived in Taqqiyyah in defense of their lives and villages. Their only sign was simply terms and greetings that allowed Shi'i to recognize one another. Khawarij on the other hand, had a different association and stereotype to them. Khawarij were seen as simultaneously religious zealots and (contradictory) as ruthless and irreligious criminals.
An actual Khawarij was infact rare in the sense that one claimed to be of the Shurha (the buyers, for they bought the heaven with the sale of the earth). The vast majority of people I would term such in this period, would fall under a diverse set of views and social status that etched groups together. Instead, most Khawarij groups and were instead formed under an almost anarchic nature and possibly capitalist outlook on the issues of Islam in the IX-X century. This included a rejection of governmental power in the way of taxation (as such was invalid) and the rejection of racial hierarchy common in Abbasid period Iraq. Combined with this, was an almost racketeering and criminal undertone, which formed republics on the foundation of a racket and or place of refuge for criminal elements in the Islamic society (notice, within shariah, a slave that escapes is a criminal).
This too though, was justified by the Khawarij through aspects of religion. Namely, the purity of their cause of rejecting the rule of a prince or the insistence that the prince is a servant of the people. Thus, the Khawarij of this period combined a sort of religious purity (an aspect of the original Khawarij during the Umayyad period) and libertarian with that of a general trend of entrepreneurial poor and criminal underground's (rackets) to reject general state structures in favor of association with quasi states and proto revolutionaries. This conception and movement mobilized in an unstoppable force in the 860s under the banner of slave revolt and destruction of plantation and mining economy of Iraq. This slogan however was only the purist side of the coin, the other side was the anarchic aspect of removing large government structures so that what could be called rackets could operate as quasi states.
The Zanj rebellion was this mobilization. It's rebellion lead to a conglomeration of revolutionaries, slaves, criminals, murderers, thieves, mercenaries, Khawarij zealots, men and women seeking adventure and a piece of the insatiable fruit of loot and vice. Coming together, was a diverse swirl of people of vastly different ideas and views. Yet, astonishingly, as if Spartacus revived, this movement created a state structure to a sort before succumbing to Abbasid pressure after a concerted counter offensive by the Abbasid in the 880s. This rebellion had the effect however, of destroying vast tracts of rural areas in the south of Iraq and southwest of Iran (Khuzestan) and filling the entire area with bandits, river pirates and criminal clans operating in the marshes of Iraq south of Baghdad.
This diverse group of Zanj holdovers and opportunists simply drawn by the carnage wrought, created an odd clique in the Batihah Sawad. A clique that created what could be termed, a state based off what was a criminal underground. This state became legendary in the time, a mythical power deep in the swamp, a land of cut throat criminals to some and to others a land of freedom from the stately oppression of the Islamic world. Buyyid powers tried in vain to defeat this so called criminal confederation, but generally were defeated in battles by the groups within the canals and swamp thickets. This infact, was a serious point of Buyyid weakness, an inability to quell rebellion not but 150 km from the city of Baghdad. This Batihah Sawad criminal confederacy, could last indefinitely and continually reform without a powerful empire like the Saljuqs rising from the east. If the current situation remains, this is interestingly, an unmovable situation in the fringes of the Iraqi river basin.
The Armenians were already free at this point virtually from Byzantium, and served as a first line of defense from Islamic forces to the south and east. Their militia are fearsome and numerous, sometimes gathering larger forces of irregular fighting men than the entire Byzantine army. These irregulars in the period following the 860s, had torn apart Islamic forces in the area and built powerful fortresses to hide within in times of war, forcing Islamic armies to return with minimal loot. These militia and princes of Armenia where still under nominal allegiance to Byzantium. Thus, they accepted being disarmed by them without much fighting prior to the Saljuq invasion.
This transgression was one of the greatest blunders of the massive bureaucracy of bloated and decadent civil servants in abundance in Constantinople. In one swoop, Byzantium alienated their greatest military asset (even more so than Anatolia in my opinion). Why they did this is beyond me, however, it can be assumed the bureaucrats of Constantinople saw the military outside of mercenaries as their enemies. Thus, Armenians, who to them were far from the capital, were dangerous with such weapons and militia. It was a complete lack of understanding and overreaching policy to infringe on the right of defense and ancient tradition of Armenians to wage incessant warfare against the enemies to the south and east. This blunder led directly to what can be seen as both a utter defeat in the east by the Saljuqs who utterly slaughtered the disarmed Armenian militia and a partial surrender of Armenians to spite Byzantium.
Regardless of the Saljuq, the Armenians will be disarmed in due time or rebel with extreme zeal against the Byzantines, or too, a power will taste the unbearable allure of a defenseless frontier. Byzantium has a tract record of this sort of blunder, that is alienating armed minorities on their frontiers. The other example is the Manichaen Paulicians who were ruthlessly persecuted by Byzantine authorities. That same Paulician community, was soon armed and now formed a major contingent in Islamic armies in Anatolia in the 800s. These Paulicians, would be a stalwart and zealous (more so than the Muslim) fighting force for the Abbasid for a century of warfare against Byzantium. The same can happen for the Armenians.
Byzantium still is in for a decline of great proportions if they do not rectify the issues I see. Namely, the two pronged case of extremely powerful nobles squatting the land of Anatolia and that of a massive and overbearing state structure. Julius Norwich infact compared Byzantium to socialism (for better lack of terms) in the sense of controlling every aspect of people's lives generally. Peasant's movement was tightly controlled by Byzantium, supposed purges of villages occurred, taxes were high, state control of the land was absolute as it could be in the Middle Ages. This peculiar situation was due to a beyond advanced bureaucracy and civil service which had an almost pathological hatred and loathing of the Anatolian military general and military brass. This led to seemingly absolute power of the civil service and subjugation of both military and navy of Byzantium. It was to me, an empire living on fumes....
Luckily for Rome in the East, so too is the Fatimids who despite their great infamia, sit weakly in Cairo. A sign of weakness if the Fatimids is their reliance on foreign subversion as opposed to the most direct way, conquest by arms. They feared the Abbasids and their protectors, as well as mutiny amongst their nominal allies in Arabia and Iraq. It should be noted, that the Fatimids at its heart was an empire in the heart of the Umayyad, which means their geopolitical compass was always to compete in the sea as opposed to engaging the powers of the east.
Essentially to wrap the Mid East up, we have a political situation of two seemingly powerful monsters (Fatimid and Rome of the East) and then many weak powers. I doubt the Byzantines can seriously defeat the Fatimid in central Syria and certainly not in Lebanon. It is almost a fluke that the Byzantines continued rule over Antioch until the Saljuq arrived and it attests to the paralysis gripping the Fatimids of the period and their allies. The only way I can imagine the Byzantines coming out on top is if they find a way to garner support from the Abbasids (not Buyyids) or play off the religious strife of the Fatimid hegemony. Fatimids on the other side, have no way to do serious damage to Byzantium without something massive occurring. It wound require a say, victorious Norman conquest in Greece, to allow for a Fatimid restoration of Islamic power in the Taurus mountain range.
The fate of the Ghaznavids is an interesting one of itself. Ghazna was a state based upon one principle, war. It sought the loot of the world and gained wealth beyond their dream and praise from across the Islamic world. In a time of extreme strife for Islam, when the world and Allah seemingly crashed, the hope was in the victorious armies of the east. Mahmud Ghaznavid created an enduring model, one of exposing the rich and seemingly endless loot and slaves of Hindustan. From this point onward, Turks marched to Wazirastan along with people from across the Islamic world, to gain a fortune. Every year, the Ghaznavids invaded and every year defeated the disorganized Hindu kingdoms.
This continued conquest however hit severe road blocks with the Rajput alliances that formed as noble warriors from the highest castes to fight the invaders. These Rajput were fearsome and in the words of a Muslim, the most skilled in the ways of the sword and indomitable in the duel of men. However, by the time of the Saljuq height, this Ghaznavid threat had transformed into what it was at its base...
At its base, the Ghaznavids were a Turkic state that for its time held a monopoly on the raiding into Hindustan. It was not a state in the same way as the Buyyid, who defended another state or the Abbasid which was a legitimate state. At each stage, the Ghaznavid gave free reign and privilege to other Turkic clans, tribes and Mamluks to continue raids. Thus, enclosing over time, their ruling caste in their homes in Afghanistan away from the front line brutality of the Rajput-Turkic warfare and the wars of loot and domination raging. The most enigmatic and future successor of the Ghaznavids was the Ghurids, who would come to break the Rajput decisively and raiding the entire Rajasthana before allocating the conquest of Northern India to a conglomerate of Mamluks who proceeded to truly break Hindu power conquering within two decades, the entirety of the Ganges river valley from Delhi to Burma.
There is no reason this will change from my understanding. Only perhaps a longer lasting Ghaznavid power centered in Afghanistan and Khursan, with the eventual Ghurids or another clan ruling modern Northern Pakistan and then another breakoff breaking through Delhi and across the Gangetic plain eastward.
Without the Saljuqs, the Anishtunginid Mamluk clan will not be slaves of the Saljuq and thus there will be no Kwarezmshahs. Instead, this area will come to be ruled by Turkic remnants of the defeated Saljuq (defeated by Ghaznavids). These Turks would quickly come under the suzerainty of the Qhara Qhabid who rule from the edges of the Song Dynasty and south of the Mongol magnates. These Turks and Qhara Qhanid, could become the new envoy of doom for Iran, which is simply open for conquest. Qhara Qhanids were exceedingly powerful, but somewhat weaker than the later Qara Qitai. Regardless, such a nomadic force is always to be reckoned with. I can see either filling either a role as ruler and destroyer of Ghaznavid power and filling the shoes of the Kwarezmshahs or becoming like the Pechenegs and essentially raiding and looting constantly and warring for hire (this is what the Qara Qitai did until they joined the forces of Temujin).
Hope this answered some questions you had and stimulated interest in this time period. Sorry for my delay
@LSCatilina , I have been mildly busy.