President John Tyler's pursuit of Texas annexation threatened the unity of both major parties. Annexation would geographically expand American slavery. It also risked war with Mexico while the United States engaged in sensitive possession and boundary negotiations with the United Kingdom, which controlled Canada, over Oregon. Texas annexation thus posed both domestic and foreign policy risks. Both major parties had wings in the North and the South, but the possibility of the expansion of slavery threatened a sectional split in each party. Expelled by the Whig Party after vetoing key Whig legislation and lacking a firm political base, Tyler hoped to use the annexation of Texas to win re-election as an independent or at least to have decisive, pro-Texas influence over the election.