Final answer:
Sargon moved his armies to conquer and unite the southern Sumerian city-states with Akkad, forming the first major empire in Mesopotamia by forcefully integrating various regions under his control.p[tion a is correct.
Step-by-step explanation:
The reason Sargon moved his armies from northern Mesopotamia into southern Sumerian city-states was a) To conquer and unite them with Akkad. Sargon, recognized as Sargon the Great or Sargon of Akkad, was the initiator of the world's first empire by conquering not only the Sumerian city-states but also territories that would comprise today's northern Iraq, Syria, and southwestern Iran. This move towards unification was a product of his desire to create a vast empire, which involved the military conquest and subsequent administrative consolidation of these regions. His empire is known for having absorbed different cultures and established a model of imperial administration that would influence later empires.
That Sargon aimed to conquer and unite is evidenced by his establishment of the world's first standing army, which exerted control over the conquered cities and fortified his rule. Sargon's administrative strategies, including the appointment of governors and the extraction of wealth to fuel the capital of Akkad, showcase an intention focused on consolidation and control, rather than cooperative kingdom-building or simply aiding in defense against foreign threats.