Nineteenth century isolationism was based largely in the Monroe Doctrine. This doctrine limited the American sphere and influence to the territorial United states and served to deter European interference in the affairs of the continent. This was a necessary deterrent in an age marked by European empire, especially the Spanish conquest and expansion in Central and South America, Russia declarations regarding areas north of the fifty-first parallel and extending one hundred miles into the Pacific would be off limits to any foreign powers. The idea that European powers control any part of American soil was abhorrent to American policymakers. Isolationism for Americans was also related to the fact that Americans were settling the continent for much of the nineteenth century and trying to establish territorial sovereignty. This situation was compounded by the War of 1812, The Seminole Wars in the 1820s, The Mexican American War in the 1840s, and the Civil War in the 1860's. Utah was the last state admitted to the Union in 1896. It is not surprising that U.S. involvement in the Spanish American War (1898) inaugurated a period of increased involvement by the United States in hemispheric and international affairs.
Article IV of the US Constitution establishes the responsibilities of the states to each other and the responsibilities of the federal government toward the states. Section 1 of Article IV requires that the states give “full faith and credit” to the public acts and judicial proceedings of every other state.
