[136] In his annual message to Congress in December 1845, Polk requested approval of giving Britain a one-year notice (as required in the Treaty of 1818) of his intention to terminate the joint occupancy of Oregon.[137] In that message, he quoted from the Monroe Doctrine to denote America's intention of keeping European powers out, the first significant use of it since its origin in 1823.[138] After much debate, Congress eventually passed the resolution in April 1846, attaching its hope that the dispute would be settled amicably.[139]
When the British Foreign Secretary, Lord Aberdeen, learned of the proposal rejected by Pakenham, Aberdeen asked the United States to re-open negotiations, but Polk was unwilling unless a proposal was made by the British.[140] With Britain moving towards free trade with the repeal of the Corn Laws, good trade relations with the United States were more important to Aberdeen than a distant territory.[141] In February 1846, Louis McLane, the American minister in London, was told that Washington would look favorably on a British proposal to divide the continent at the 49th parallel.