The Monroe Doctrine asserted that the American continents, by their free and independent condition, were no longer to be considered subjects for future colonization by any European powers. It held that the United States had never taken part in wars among European powers over matters relating to themselves and that doing so did not accord with its policy. It also declared that the United States would resent injuries or prepare for its defense only when its rights were invaded or seriously menaced, and that any attempt by European powers to extend their system to any portion of this hemisphere would be considered dangerous to its peace and safety.