Manifest Destiny was a term coined by American newspaper editor John L. O'Sullivan in 1845 to describe the idea that the United States was destined to expand across North America. The Louisiana Purchase of 1803 doubled the size of the U.S. and gave it important trade routes, representing the first major step of westward expansion. Manifest Destiny played a key role in boundary disputes with Britain over Oregon and the annexation of Texas, which led to the Mexican-American War after President Polk moved into a disputed area between Texas and Mexico. While expansion was seen as America's destiny by some, critics viewed it as an attempt to take land from other peoples through greed and desire for control.