A) Louisiana Purchase Treaty of 1803 INCORRECT The Louisiana Purchase was a land deal between the United States and France, in which the U.S. acquired approximately 827,000 square miles of territory west of the Mississippi River for $15 million. This treaty doubled the size of the U.S. and opened up vast areas for westward expansion, but it was a specific territorial acquisition, not a general foreign policy doctrine. It did not address European colonization or interference in the Americas as a whole. While it was a major executive action by President Thomas Jefferson, it lacked the broad policy implications of the Monroe Doctrine.
B) Adams-Onís Treaty of 1821 INCORRECT Also known as the Transcontinental Treaty, this agreement between the U.S. and Spain ceded Florida to the United States and defined the boundary between the U.S. and New Spain (now Mexico) from the Gulf of Mexico to the Pacific Ocean. It was negotiated by Secretary of State John Quincy Adams and resolved long-standing border disputes, but it was a bilateral treaty focused on territorial issues, not a unilateral policy declaration about European influence in the Western Hemisphere. It did not establish a broad stance against European colonization.
C) Monroe Doctrine of 1823 CORRECT The Monroe Doctrine was articulated by President James Monroe in his annual message to Congress on December 2, 1823. It declared that the United States would view any European attempt to colonize or interfere with independent nations in the Americas as a hostile act. The doctrine was a bold assertion of U.S. influence in the Western Hemisphere and became a fundamental principle of American foreign policy. It was prompted by concerns over Russian claims in the Pacific Northwest and the possibility of European intervention in Latin America. While initially unenforceable, it was later backed by U.S. military power and used to justify interventions in the Caribbean and Central America. The doctrine has had a lasting impact, shaping U.S. relations with Latin America and serving as a basis for the Roosevelt Corollary and other policies.
D) Treaty of Guadalupe-Hidalgo of 1848 INCORRECT This treaty ended the Mexican-American War and ceded a vast territory to the United States, including present-day California, Nevada, Utah, Arizona, New Mexico, and parts of Colorado and Wyoming. In exchange, the U.S. paid $15 million and assumed claims of American citizens against Mexico. This treaty was a significant territorial expansion, but it was a specific peace agreement, not a policy doctrine. It did not address European colonization or set a precedent for U.S. foreign policy in the way the Monroe Doctrine did.
