He proved much harder on Mexico. When Santa Anna refused Polk’s offer to buy California for chump change, Napoleon of the Stump sent the US Army across the Rio Nueces into Mexico. When Santa Anna’s troops tried to resist, Polk lied to Congress, claiming that our southern neighbors had “shed American blood on American soil.” This secured a declaration of war and prompted a full-scale invasion. After US forces stormed the Halls of Montezuma, Polk stole the northern half of Mexico.
…rrender all of the Oregon Country to the United States (at the time a military and naval weakling). London called Polk’s bluff, kept British Columbia, and let the US have what is now Oregon, Washington and Idaho. Polk prudently took the deal.