The Transcontinental Treaty of 1819 gave the United States a solid diplomatic claim on the territory abutting the Pacific Ocean. Many in the Democratic Party, such as James K. Polk (1795–1849), sought further continental expansion by diplomacy or conquest; but the rival Whig Party, especially Daniel Webster (1782–1852) and later William Seward (1801–1872), feared this would exacerbate the national division over slavery. They preferred economic rather than territorial expansion, notably by extending U.S. commercial opportunities in the Pacific. To reach these markets and fish these seas the United States needed to secure a maritime route to Asia. One key to this route was the Hawaiian, or Sandwich, Islands—the “Malta of the Pacific”—which already had considerable economic value. Hawaii was governed by an independent native monarchy, but New England whaling vessels had long made use of the islands, Protestant missionaries had been present there for several decades, and American merchants were engaged in the sugar trade.
The geographic location and economic importance of the islands also attracted the attention of Britain and France. Webster, then secretary of state, persuaded President John Tyler (1790–1862) to extend the Monroe Doctrine’s opposition to European interference in Western Hemispheric to include Hawaii, which Tyler did in his Special Message to Congress in December 1842. Although the United States did not engage in a proposed tripartite agreement with London and Paris to guarantee the islands’ independence, the Tyler Doctrine did claim special U.S. interests based on proximity and trade, and made clear that if other powers threatened Hawaii’s independence the United States would be justified in “making a decided remonstrance.” Seeking to protect U.S. interests at minimum cost, the doctrine claimed Hawaii as a U.S. sphere of influence and firmly supported its independence, establishing a policy that would last until annexation in 1898.