The battle of Manzikert, in 1071, is often cited as a decisive Turkish victory in which the back of the Eastern Roman Empire was shattered, but from what I can see, actual territorial changes didn't start happening until 1073-74. Was Manzikert really such a crushing blow, and if so, why the lull until territory started changing hands?
Well it depends on which perspective you are referring to. As I know the Seljuk side the best, I can answer from that direction.
Manzikert, in my opinion, was not an important battle for the Seljuks. It was considered a minor battle, at least by the Seljuks, who were on the way to fight a more important battle against the Fatamids. The conflict between the two began as a series of raids by the Turkmen which in response the Byzantines led the army to stop these raids.
After the battle, there were a number of factors which led to the delay of the actual movement of Turkmen tribes into the area. Firstly, Alp Arslan, died in 1072 CE while in Central Asia where he was trying to conquer his ancestral home. Therefore, the majority of the army was in Central Asia and far from Anatolia.
Secondly, a nomadic empire needs to continually direct its energies towards conquest otherwise that state becomes rebellious and instability reigns. By the time that Malik-Shah I had solidified his control of the throne and relative stability had returned, the Seljuk state was in a position to divert the Turkmen tribes towards Anatolia to stabilise the state. Therefore, why you see a delayed expansion of Turkmen into Anatolia.
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