But still worse for the Latins was the capture of Jerusalem by the Seljukian Turks in 1071.
The Seljukian Turks, first the mercenaries and then the masters of the caliph, had given new life to the decadent caliphate of Bagdad.
The Seljukian sultans had only achieved a military occupation of the country which they had conquered.
Accordingly, when the crusaders had captured the town at Nicaea, and defeated the Seljukian field-army at Dorylaeum their way lay clear before them through Asia Minor.
Of Asia Minor, which survived unsubdued in the general deluge of Seljukian conquest, they could expect active assistance (the hope of which will explain the north-easterly line of march which they followed after leaving Heraclea).
But the purely military character of the Seljukian occupation helped the crusaders in yet another way.
On the death of Malik Shah, the last of the great Seljukian emperors (1092), the empire dissolved.
Not only was Syria thus weakened by being detached from the body of the Seljukian empire; it was divided by dissensions within, and assailed by the Fatimite caliph of Egypt from without.
The atabegs formed a number of dynasties, which displaced the descendants of the Seljukian amirs in their various principalities.
The Crusades began with the Seljukian Turk planted at Nicaea; they ended with the Ottoman Turk entrenched by the Danube.
In that year a horde, variously estimated at from two to four thousand souls, with their flocks and their slaves, driven originally from their Central Asian homes by the pressure of Mongol invasion, and who had sought in vain a refuge with the Seljukian sultan Ala-ud-din Kaikobad of Konia, were returning under their chief Suleiman Shah to their native land.
The help afforded by Ertoghrul to the Seljukian monarch on a critical occasion led to the addition of Sugut to his fief, with which he was now formally invested.
In 1300 the Seljukian Empire crumbled away, and many small states arose on its ruins.
At that time a number of principalities had replaced the Seljukian state.
Though Yahsha Bey, grandson of Mahommed Karaman Oghlu, had declared himself the successor of the Seljukian sultans, the princes of Aidin, Sarukhan, Menteshe, Kermian, Hamid, Tekke and Karassi declined to recognize his authority, and considered themselves independent, each in his own dominions.
At his accession Orkhan was practically on the same footing with these, and avoided weakening himself in the struggle for the Seljukian inheritance, preferring at first to consolidate his forces at Brusa.
In the same year Bey Shehr and other portions of the Hamid principality were acquired by purchase from their ruler Hussein Bey, as the Karamanian princes were beginning to cast covetous eyes on them; but the Karamanians were unwilling to resign their claims to be heirs of the Seljukian sultans, and not until the reign of Mahommed II.
Hence the vast majority of the people whom we are accustomed to think of as Ottomans are so only by adoption, being really the descendants of Seljuks or Seljukian subjects, who had derived from Persia whatever they possessed of civilization or of literary taste.
In 1040 the Seljuk Turks crossed the Oxus from the north, and having defeated Masud, sultan of Ghazni, raised Toghrul Beg, grandson of Seljuk, to the throne of Persia, founding the Seljukian dynasty, with its capital at Nishapur.
The Seljukian empire had, after 1076, been divided and subdivided among Turkish atabegs.
This excited the jealousy of Toghrul Beg, who summoned him to give up Hamadan and the fortresses of Jebel; but Ibrahim refused, and the progress of the Seljukian arms was for some time checked by internal discord - an everrecurring event in their history.
The Seljukian dynasty of Syria came to an end after three generations, and its later history is interwoven with that of the crusaders.
Nevertheless the Seljukian dominion was petty and unimportant and did not rise to significance till his son and successor, Kilij Arslan II., had subdued the Danishmands and appropriated their possessions, though he thereby risked the wrath of the powerful atabeg of Syria, Nureddin, and afterwards that of Saladin.