In 1846, most Americans supported a war with Mexico hoping that it would settle boundary disputes and increase the United States' territory. Why didn't American abolitionists support the Mexican-American War?

They did not want slaves to be drafted into the military.

A Mexican win would force every American state to adopt slavery.

They did not want slavery to extend to new areas of the United States.

Abolitionist groups would weaken if too many of their members went away to war.

American abolitionists did not support the American-Mexican war because they did not wanted slavery to extend to new areas of the United States.

Explanation:

American abolitionists attacked the war as an attempt by slave-owners to strengthen the grip of slavery and thus ensure their continued influence in the government. It was predicted that, "The United States will conquer Mexico, but it will be as a man who swallowed the arsenic which brings him down in turn. Mexico will poison us."

The expansion of slavery in the lands seized from Mexico fueled the drift to civil war just a dozen years later. Prominent artists and writers like Transcendentalist writers, Henry David Thoreau and Ralph Waldo Emerson opposed the war. Also an essay now known as Civil Disobedience was written in this regard.