During the mid-1800's Monroe's declaration which combined with the ideals of Manifest Destiny, provided guidance and support for the United States' expansion on the American continent. In the late 1800's the United States' economic and military power enabled it to enforce the Monroe Doctrine. But it was Theodore Roosevelt's Corollary that greatly extended it. The Doctrine, issued by President James Monroe in 1823, had basically warned European powers not to interfere in the Western Hemisphere's affairs. Its three main concepts included non-colonization, non-intervention, and separate spheres of influence for the Americas and Europe. Forty years later, in 1904, it was invoked when European creditors of a few Latin American countries, threatened armed intervention to collect debts.
With the economic decline of several Latin American nations, European intervention resurfaced as an issue in the United States' foreign policy when European governments began to use force to pressure on these into paying their debts.
Along with a crisis between the Dominican Republic and its European creditors came a blockade along Venezuela's coast in 1902, erected by naval forces from Britain, Italy and Germany. This greatly alarmed President Theodore Roosevelt. He along with many Americans feared that European nations might intervene forcibly to collect their debts and eventually take over. Immediately he warned these to withdraw.
With this, he "updated" the Monroe Doctrine with his new corollary. It was rather an addition or appendix to the Monroe Doctrine. In it Roosevelt proclaimed that it was the United States' right to monitor and therefore restrain such unlawful activity. In his annual message to Congress he announced, "chronic wrongdoing... may in America, as elsewhere, ultimately require intervention by some civilized nation, and in the Western Hemisphere the adherence of the United States to the Monroe Doctrine may force the United States, however reluctantly, in flagrant...