Why might it threaten the US to have new european colonies near them?

Answer 1

President James Monroe first proclaimed the Monroe Doctrine in 1823 to establish a U.S. sphere of influence in the Americas. At this time, Bolivia and several Caribbean islands remained under Spanish control, notably Cuba and Puerto Rico. The United States worried that if Spain lost control of these colonies, France or Britain might gain them.

Secretary of State John Quincy Adams discussed these concerns in a letter to his friend, Hugh Nelson. He wrote that, "Such indeed are, between the interests of that island and of this country, the geographical, commercial, moral, and political relations, formed by nature, gathering in the process of time, and even now verging to maturity, that in looking forward to the probable course of events for the short period of half a century, it is scarcely possible to resist the conviction that the annexation of Cuba to our federal republic will be indispensable to the continuance and integrity of the Union itself."

The United States was also worried about European encroachment in North America. For example, Russia was exploring the northwestern coast of the continent, something Adams expressed his concerns about to the Russian minister.

Ultimately to protect their interests, the American and British governments made a joint declaration protecting the sovereignty of independent nations in the region against France and Spain. Ultimately, the American government outmaneuvered the British by declaring that all European powers (the British included) could not encroach in the region.