Final answer:
The Monroe Doctrine, declared in 1823, opposed new European colonization in the Americas and stated the US's stance of non-interference by either the Americas or Europe in each other's affairs. Bolívar saw more weight in British influence than the Monroe Doctrine, but it nonetheless signified a shift in U.S. foreign policy and influenced later policies like the Roosevelt Corollary.
Step-by-step explanation:
The statement that declared the US would not interfere with any existing European colonies in the Americas but that it would oppose new colonies is known as the Monroe Doctrine. President James Monroe outlined this doctrine in his annual message to Congress in 1823 after consideration by U.S. Secretary of State John Quincy Adams, who believed it important for America to express its own principles rather than follow the lead of Great Britain. The Monroe Doctrine was a significant element of U.S. foreign policy, asserting that future European colonization in the Western Hemisphere was unacceptable, and that American and European political systems were distinct, advising non-interference by either party in the other's affairs.
While the US expected to deter European involvement in the Americas, it also recognized the importance of maintaining peace and trade in the region. Latin American revolutionary leader Bolívar perceived British support to be more influential than the Monroe Doctrine in holding off Spanish colonial ambitions. Nonetheless, the doctrine marked a pivotal moment in American foreign policy, underscoring the nation's growing sense of uniqueness and its geopolitical interests in the Western Hemisphere. Later, the Roosevelt Corollary in 1904 expanded upon the Monroe Doctrine, asserting a more interventionist U.S. role in the Western Hemisphere to provide assistance to nations deemed in need.