Final answer:
In the film Avatar, the methods used by characters are fictional and based on plot development rather than historical fact. Nevertheless, ancient city-states and empires often used intermarriage and tribute as peaceful means to acquire territory.
Step-by-step explanation:
The student's question addresses the plot of the movie Avatar, in which Colonel Quaritch convinces Parker Selfridge to escalate military action against the Na'vi. This is not an actual historical event but part of a film's storyline. As such, it does not directly relate to reality but rather to the themes of colonization and military intervention depicted in the film. However, regarding ancient city-states and empires acquiring territory through peaceful means, one method they commonly used was intermarriage. Through marriages between different royal families or powerful houses, entities could solidify alliances and claim rights over territories without resorting to warfare. Another peaceful means was the payment or receipt of tribute, where one state would pay another to acknowledge their supremacy, but without direct control over their territory. It was a way of demonstrating power and influence without conquest.