Facing a hostile Congress, Tyler and Webster turned their attention to foreign policy. The administration put a new emphasis on American influence in the Pacific Ocean, reaching the first U.S. treaty with China, seeking to partition Oregon Country with Britain, and announcing that the United States would oppose any attempt to colonize the Hawaiian Islands. The most pressing foreign policy issue involved relations with Britain, as the United States had nearly gone to war with Britain over the Caroline affair and a border conflict between Maine and Canada. Seeking improved relations with the United States, British Prime Minister Robert Peel dispatched Lord Ashburton on a special mission to the United States. After extensive negotiations, the United States and Britain reached the Webster–Ashburton Treaty, which clearly delineated Maine's northern border and other sections of the U.S.-Canada border that had been in dispute. Senator Thomas Hart Benton led Senate opposition to the treaty, arguing that it "needlessly and shamelessly" relinquished American territory, but few others joined Benton in voting against the treaty, and it won ratification.