This treaty was rejected by the Whigs, mainly as a show of hostility toward the Tyler administration. In an 1842 special message to Congress, the president also applied the Monroe Doctrine to Hawaii (dubbed the "Tyler Doctrine"), told Britain not to interfere there, and began a process that led to the eventual annexation of Hawaii by the United States. In 1842 Secretary of State Daniel Webster negotiated with Britain the Webster–Ashburton Treaty, which determined the border between Maine and Canada. That issue had caused tension between the United States and Britain for decades and had brought the two countries to the brink of war on several occasions. Though the treaty improved Anglo-American diplomatic relations, Tyler was nevertheless unsuccessful in concluding a treaty with the British to fix the boundaries of Oregon. On Tyler's last full day in office, March 3, 1845, Florida was admitted to the Union as the 27th state. Tyler advocated an increase in military strength and this drew praise from naval leaders, who saw a marked increase in warships. Tyler brought the long, bloody Second Seminole War to an end in 1842, and expressed interest in the forced cultural assimilation of Native Americans. He also advocated the establishment of a chain of American forts from Council Bluffs, Iowa to the Pacific. In May 1842 when the Dorr Rebellion in Rhode Island came to a head, Tyler pondered the request of the governor and legislature to send in federal troops to help suppress it. The insurgents under Thomas Dorr had armed themselves and proposed to install a new state constitution. Before such acts, Rhode Island had been following the same constitutional structure that was established in 1663. Tyler called for calm on both sides, and recommended that the governor enlarge the franchise to let most men vote. Tyler promised that in case an actual insurrection should break out in Rhode Island he would employ force to aid the regular, or Charter, government. He made it clear that federal assistance would be given only to put down an insurrection once underway, and would not be available until violence had taken place. After listening to reports from his confidential agents, Tyler decided that the 'lawless assemblages' had dispersed and expressed his confidence in a "temper of conciliation as well as of energy and decision" without need of federal forces. The rebels fled the state when the state militia marched against them, but the incident led to broader suffrage in the state. Two vacancies occurred on the Supreme Court during Tyler's presidency, as Justices Smith Thompson and Henry Baldwin died in 1843 and 1844, respectively.