The Roosevelt Corollary
Theodore Roosevelt announced an addition to the Monroe Doctrine. He stated, in referring to South and Central America, that the United States had the right and the need to intervene in the internal affairs of states in the Western hemisphere if they did not get their own affairs in order.
From late 1902 to 1903 Britain, Germany and Italy imposed a naval blockade on Venezuela as a result of its failure to pay debts to their citizens. An international court decided that the countries that were blockading were preferred creditors, something that the United States objected to, fearing that it would lead to other countries intervening in Western Hemisphere affairs in order to become the preferred creditors.
To solve this problem President Roosevelt presented a radical solution. The United States would intervene in the internal affairs of countries in the Western Hemisphere if they were not able to get their own fiscal house in order, that way they would block the possibility of European states intervening.
President Roosevelt stated the following in his annual message to Congress in 1904
All that this country desire is to see the neighboring countries stable, orderly, and prosperous. Any country whose people conduct themselves well can count upon our hearty friendship. If a nation shows that it knows how to act with reasonable efficiency and decency in social and political matters, if it keeps order and pays its obligations, it need fear no interference from the United States. Chronic wrongdoing, or an impotence which results in a general loosening of the ties of civilized society, 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 cases of such wrongdoing or impotence, to the exercise of an international police power.
This was the Roosevelt Corollary and it became the basis of numerous American interventions in South and Central America in the first decades of the 20th century.