Question

one reason thoreau opposed the mexican-american war was that he believed it
would eliminate slavery in the united states.
was fought to add more states where slavery would be legal.
would take the lives of his fellow citizens.

Explanation:

Thoreau opposed the Mexican-American War primarily because he viewed it as a plot by pro-slavery forces to expand the territory where slavery was legal, extending the institution's reach rather than limiting it. Concerns about citizen deaths were not his core stated reason, and he did not believe the war would end slavery.

Answer:

was fought to add more states where slavery would be legal.