Why might it threaten the United States to have new European colonies near them?

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."