The correct answer is: "economic stability".
Primitive civilations became sedentary when they learnt how to grow crops (agriculture) and animal husbandry practices, and they could substitute the previous way of obtaining food by hunting, fishing and gathering, that required them to be nomadic people.
In the new settlements, specialization and division of labor appeared. Some people manufactured tools, others worked in the fields and others kept going hunting, fishing and gathering in order to have alternative food reserves. Such structure started to demand a political class, to organize the different tasks.
Moreover, such efficiency and the technological revolution connected to the usage of tools, allowed to obtain production surpluses (not only food for subsistence) and trade activities with other tribes and settlements flourished. Therefore, the need for authorities became even more urgent, as it was crucial to have representatives that could make decisions, negociate with other tribes, organize the different jobs that needed to be done, etc.
