Since its birth as a nation, the United States has espoused an imperialist vocation rooted in the universalism of republican principles. These principles inspired the Monroe Doctrine and the big-stick policy and turned the nation into an international police force. From the end of World War II to the collapse of the socialist bloc, U.S. security policies in Latin America led to interventions directed against insurgency. In the post-cold war context, interventionism has also played a key role in Colombia, where a policy based on the war against drugs was maintained until 2001. Since the September 11, 2001, attacks, the United States has geared its national security policies toward fighting the terrorist threat.