"The North" qualifies as such. At a time when slavery was becoming a hot issue in American politics, they were afraid "The South" would use the newly conquered territories to increase slavery and get the upper hand.
You should be aware that the Mexican-American War (1846-1848) was an extension of the Texas Revolution (1835-1836) which was by itself, motivated by slave owners.
Northern abolitionists opposed the Mexican American War.
The Whigs.
Yes, Lincoln was against the War with Mexico.
People were opposed to the annexation of Texas because it would be admitted to the union as a slave state.
because they thought it would be easier to defeat them so the war could end quickly
Socialists
abolitionists
Democrats
United States, Ecuador, MEXICO, Guatemala, Honduras
The Industrial Workers of the World
reservationists
The fear that slavery would spread into new territories