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   The history of the United States Marine Corps began with the founding of the Continental Marines on 10 November 1775 to conduct ship-to-ship fighting, provide shipboard security and discipline enforcement, and assist in landing forces. Its mission evolved with changing military doctrine and foreign policy of the United States. Owing to the availability of Marine forces at sea, the United States Marine Corps has served in nearly every conflict in United States history. It attained prominence when its theories and practice of amphibious warfare proved prescient, and ultimately formed a cornerstone of the Pacific Theater of World War II. By the early 20th century, the Marine Corps would become one of the dominant theorists and practitioners of amphibious warfare. Its ability to rapidly respond on short notice to expeditionary crises has made and continues to make it an important tool for American foreign policy.[1]

More info here>http://en.wikipedia.org/wiki/History_of_the_United_States_Marine_Corps