Answer:
The correct answer is A) power
Step-by-step explanation:
The sentence expresses a relation between the Comanches-Kiowa alliance in the territory of the southern Plains. In this context, dominion means that they governed and exercised power in that territory. They didn't just oversee the Plains and didn't need superiority in order to have control over the region but they had the authority to rule. Thus, in this sentence, dominion means power.