Answer:Despite the acceptance by many Americans in the 1840s of the concept of Manifest Destiny—that it was the providential right of the United States to expand to the Pacific Ocean—the future boundary between the United States and Mexico was anything but a foregone conclusion. Great Britain, with whom the United States shared possession of the Oregon Country, was part of the equation. Some influential Americans were convinced that the British were determined to block U.S. expansion to the Pacific by gaining control of California from Mexico. In 1846, however, Britain’s ambitions in the region became clearer when the U.S. and Britain agreed upon the 49th parallel (the present border between the U.S. and Canada) as the permanent boundary between their lands in the Pacific Northwest. Still, U.S. Pres. James K. Polk remained determined to expand the country’s territorial limits.
Mexico–United States relations (Spanish: Relaciones México-Estados Unidos), also knows as Mexican-American relations, refers to the bilateral relations between Mexico and the United States. The two countries share a maritime and land border. Several treaties have been concluded between the two nations bilaterally, such as the Gadsden Purchase, and multilaterally, such as the North American Free Trade Agreement. Both are members of various international organizations, including the Organization of American States and the United Nations.