Answer:
Once there was a food surplus, complexity within early river civilizations increased, as did __________, according to the archaeological record.
Explanation:
<u>Mesopotamia, land between rivers, its economy, as in many other fluvial civilizations, was based mainly on agriculture</u>. <u><em>The first Neolithic settlements settled in fertile areas, generated surplus agricultural and livestock</em></u> that allowed them a progressive increase in population, <em><u>crafts, and trade.
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<em><u>This transformation required the control of the course of the rivers to guarantee the crops</u></em>.
<u><em>The answer is</em></u>: <u>The population.</u>