President Polk spent most of his time in office dealing with foreign affairs. In fact, the term “Manifest Destiny” is often mentioned when discussing Polk. Manifest Destiny is the idea that it was the destiny of the United States to span from the Atlantic to the Pacific. This view was held by Polk and those of his time as they worked to consolidate the territories that would eventually become the present-day United States.
IN THEIR OWN WORDS…
Polk during his inaugural address: “[E]ighty years ago our population was confined on the west by the ridge of the Alleghenies. Within that period … our people … have filled the eastern valley of the Mississippi, adventurously ascended the Missouri …, and are already engaged in establishing the blessings of self-government in valleys of which the rivers flow to the Pacific. The world beholds the peaceful triumphs of the industry of our emigrants.”
In 1846, the Oregon Treaty, which was created between the United States and Great Britain, fixed the boundary of the Oregon territory at the forty-ninth parallel. Further, Washington and Oregon would become U.S. territories while Vancouver would remain a British territory.
Mr. Polk's War
The Mexican War lasted for much of Polk's time in office, from 1846 to 1848. The annexation of Texas hurt relations between Mexico and America, and further, the border between the two countries was disputed. The United States felt that the border should be set at the Rio Grande River. When Mexico would not agree, wanting a border further north, President Polk prepared for war and ordered General Zachary Taylor to the border area. Some believe that he also wanted to go to war with Mexico as a way to gain California. Contemporary critics called this conflict “Mr. Polk's War.”America had attempted to purchase the territory twice from Mexico but was rebuffed both times. Polk's belief in Manifest Destiny would drive him to acquire as much of the North American continent as he could.
Mexican troops fired on U.S. troops in April 1846. Polk used this incident to gain a declaration of war against Mexico. The war progressed steadily, favoring the United States with American forces invading Mexico. By the end of 1847, Mexico was ready to make peace. The cost in human lives was high, many of the troops having died of disease.
Treaty of Guadalupe Hidalgo
In February 1848, the Treaty of Guadalupe Hidalgo was signed, officially ending the Mexican War. This treaty fixed the border between Texas and Mexico at the Rio Grande, as the United States wished. Further, the United States gained California and Nevada, among other present-day territories, amounting to more than 500,000 square miles of land. This was the largest increase in territory for the United States since Thomas Jefferson's Louisiana Purchase. In exchange for the concessions of the treaty, the United States agreed to pay Mexico $15 million. The agreement had the important effect of reducing Mexico to half of its former size.