The Monroe Doctrine was expanded by the Roosevelt Corollary in 1904 , providing that the United States had a right and obligation to intervene " in flagrant cases of such wrongdoing or impotence " that a nation in the Western Hemisphere became vulnerable to European control . In practice , this meant that the United States was led to act as a collections agent for European creditors by administering customs duties in the Dominican Republic ( 1905 – 1941 ) , Haiti ( 1915 – 1934 ) , and elsewhere . The intrusiveness and bad relations this engendered were somewhat checked by the Clark Memorandum and renounced by President Franklin D. Roosevelt 's " Good Neighbor Policy . " After 1947 , the U.S. poured tens of billions of dollars into the Marshall Plan , and other grants and loans to Europe and Asia to rebuild the world economy . Washington pushed hard to accelerate decolonization and bring an end to the colonial empires of its Western allies , most importantly during the 1956 Suez Crisis , but American military bases were established around the world and direct and indirect interventions continued in Korea , Indochina , Latin America ( '' inter alia '' , the 1965 occupation of the Dominican Republic ) , Africa , and the Middle East to oppose Communist invasions and insurgencies . Since the dissolution of the Soviet Union , the United States has been far less active in the Americas , but invaded Afghanistan and Iraq following the September 11 attacks in 2001 , establishing army and air bases in Central Asia
September 11 attacks
September 11 attacks
Decolonization