Answer:
What accounted for the shift was the same thing that accounted for the shift in other parts of the world: the development of agriculture.
Step-by-step explanation:
When a society develops agriculture, it shifts from being nomadic to being sedentary. This is because of two main, intertwined reasons:
The first is that growing crops is a burdensome activity that demands a lot of time, and care: ploughing the land, planting the seeds, tending the crops, caring for them, and picking them in time of harvest. This makes growing crops clash with a nomadic lifestyle.
The second reason is that agriculture is a more efficient way to produce food than hunting or gathering. Agriculture does produce a steady supply of food when the crops do not fail, while gathering and hunting hardly produces what is necessary for survival. This is an incentive for early societies to develop agriculture.