When James Monroe was elected President in 1817, the United States had recently doubled in size through the Louisiana Purchase of 1803, which Monroe had helped to negotiate, and had prevailed in the War of 1812. As such, the country was fast becoming the dominant power in the northern half of the Western Hemisphere. Simultaneously, the rest of the Hemisphere was engulfed in revolutionary wars that transformed the European colonies into independent nation-states, the same transformation in which Britain's thirteen colonies had become the United States of America. Along with most of his countrymen, President Monroe was naturally sympathetic towards the peoples of the Spanish colonies of Mexico and Central America, the French and Spanish colonies of the Caribbean, and the Portuguese and Spanish colonies of South America who had fought for their independence.
In his address to Congress in 1823, President Monroe proclaimed that the United States officially opposed any attempts by the nations of Europe to restore colonial rule over the peoples of the Western Hemisphere. In other words, President Monroe was saying to the rest of the world that, from now on, the United States was a significant power on the world stage and that any European country that attempted to re-colonize any part of the Western Hemisphere would be opposed by the United States and, therefore, risk war with the United States. This was truly remarkable considering that less than fifty years earlier the United States consisted of a tiny, weak country occupying the eastern coast of North America.