In a significant editorial published in the New York Morning News, journalist John L. O'Sullivan articulated the concept of 'Manifest Destiny,' which became a rallying cry for American expansionism. This doctrine asserted that it was the divine right and destiny of the United States to expand across the North American continent. O'Sullivan specifically argued for the full claim and control of the Oregon Country, a vast territory that included parts of modern-day Oregon, Washington, and British Columbia. His persuasive piece emphasized not only the inevitability of expansion but also framed it as a moral imperative. The Oregon Country was a point of contention between the United States and Britain, with both nations laying claim to the land. O'Sullivan's call to action came during a time when the U.S. was increasingly confident in its territorial ambitions and willing to assert its claims over territories held by foreign powers. His words resonated with a populace eager for growth and new opportunities, illustrating the national sentiment of the time and the desire to explore westward into uncharted territories.