After World War II, the Soviet Union and the United States were the two most powerful countries left in the world. The Cold War was a period of tension between the two countries over ways of life. The two countries tried to get other countries on their side.
In 1846, the United States and Great Britain signed the Oregon Treaty. In this treaty, Oregon Country was split with the U.S. gaining sole possession of the territory south of the 49th parallel, and Great Britain gaining sole possession of the land to the north.10.In 1853, the United States sent diplomat James Gadsden to Mexico to renegotiate the border between the U.S. and Mexico.. From 1818 to 1846, the United States and Great Britain administered the territory in Oregon together. This was a compromise until both countries could agree on how to divide the land between them.
When the United States admitted Texas to the Union in 1845, the Mexican government was outraged, and from 1846 to 1848, the two nation's squared off in the Mexican War. With a resounding victory, the United States gained control of Texas, New Mexico, and California. The Oregon territory was annexed in 1846 as well, and the US controlled the land all the way to the Pacific Ocean. As the population of the West soared and the prospects of statehood for western territories appeared clearer and clearer, the nation battled over the future of slavery in the West. This battle was one reason for the Civil War, which slowed the acceleration of expansion.