Canning’s overture was earnestly considered in America.  The ex-Presidents, Jefferson and Madison, recommended its acceptance, but the Secretary of State, John Quincy Adams, opposed this, favouring rather a separate declaration by the United States, and of this opinion was also President Monroe.  Thus arose the Monroe Doctrine announcing American opposition to the principle of “intervention,” and declaring that the American continents were no longer to be regarded as open to further colonization by European nations.  The British emergency situation with France, though already quieted, caused Monroe’s Message to be greeted in England with high approval.  But Canning did not so approve it for he saw clearly that the Monroe Doctrine was a challenge not merely to continental Europe, but to England as well and he set himself to thwart this threatening American policy.  Had Canning’s policy been followed by later British statesmen there would have resulted a serious clash with the United States[8].

In fact the Monroe Doctrine, imposing on Europe a self-denying policy of non-colonial expansion toward the west, provided for the United States the medium, if she wished to use it, for her own expansion in territory and in influence.  But for a time there was no need of additional territory for that already hers stretched from the Atlantic to the Rocky Mountains, two-thirds of the way from ocean to ocean.  Her population was growing fast.  But four millions at the time of the Revolution, there were thirteen millions in 1830, and of these nearly a third were already across the Appalachian range and were constantly pressing on towards new lands in the South and West.  The Monroe Doctrine was the first definite notice given to Europe of America’s preconceived “destiny,” but the earlier realization of that destiny took place on lines of expansion within her own boundaries.  To this there could be no governmental objection, whether by Great Britain or any other nation.

But when in the decade 1840 to 1850, the United States, to the view of British statesmen, suddenly startled the world by entering upon a policy of further territorial expansion, forsaking her peaceful progress and turning toward war, there was a quick determination on a line of British policy as regards the American advance.  The first intimation of the new American policy came in relation to the State of Texas which had revolted from Mexico in 1836, and whose independence had been generally recognized by 1842.  To this new state Britain sent diplomatic and consular agents and these reported two factions among the people—­one seeking admission to the American Union, one desiring the maintenance of independence.