テキサス併合
Nevertheless, Polk's aggressive expansionism has been criticized on ethical grounds. He believed in "Manifest Destiny" even more than most did. Referencing the Mexican–American War, ex-president Ulysses S. Grant stated that "I was bitterly opposed to the [Texas annexation], and to this day regard the war, which resulted, as one of the most unjust ever waged by a stronger against a weaker nation. It was an instance of a republic following the bad example of European monarchies, in not considering justice in their desire to acquire additional territory." Whig politicians, including Abraham Lincoln and John Quincy Adams, contended that the Texas Annexation and the Mexican Cession enhanced the pro-slavery factions of the United States. Unsatisfactory conditions pertaining to the status of slavery in the territories acquired during the Polk administration led to the Compromise of 1850, one of the primary factors in the establishment of the Republican Party and later the beginning of the American Civil War.