sentences:  Because of the peaceful relations between the two countries, Canada could assist Britain in a European war without having to defend itself at home.The Doctrine's authors, chiefly future-President and then Secretary-of-State John Quincy Adams, saw it as a proclamation by the U.S. of moral opposition to colonialism, but it has subsequently been re-interpreted and applied in a variety of instances.As the U.S. began to emerge as a world power, the Monroe Doctrine came to define a recognized sphere of control that few dared to challenge.