While many Southerners supported and fought in the Mexican-American War, many Northerners
opposed the conflict and referred to it as "Mr. Polk's War" because
they believed it was unwise to take on a militarily superior nation like Mexico.
O they feared that Canada might enter the conflict on behalf of Mexico.
O they suspected that the war was a blatant effort to gain more land to extend the institution of slavery.
O they were generally more pacifist than Southerners.