It is not surprising that the most important acts of American foreign policy during this period involved territorial acquisitions, the only difference being that, with the disappearance of the frontier, the object was overseas territory, and the instrument employed was the navy rather than the army. This change was influenced by the great colonial expansion undertaken by the Europeans since 1881, as well as by Alfred Thayer Mahan, the apostle of seapower. The major motivation for U.S. expansion was the search for markets in a world (Indochina, Africa, and China) being closed off by Europeans. Nevertheless, the American approach retained its versatility: treaties remained but one among several methods of annexation.
On 17 January 1878 the United States signed the Samoan Treaty with a number of tribal chiefs, thereby receiving the right to use the strategic port of Pago Pago on the island of Tutuila. The Senate gave its approval on 30 January. The Berlin Conference of 1889, involving the Americans, the British, and the Germans, resulted in an accord establishing a tripartite protectorate over the islands (14 June). On 2 December 1899 a new treaty reallocated the islands among the three powers. It was ratified by the Senate on 16 January 1900.
In the Hawaiian Islands, after numerous futile negotiations during the nineteenth century, Queen Liliuokalani was deposed in 1893 in favor of a provisional revolutionary government. The latter (composed mainly of Americans) proposed a treaty of annexation by the United States (14 February 1893), which was rejected by President Grover Cleveland. The Republic of Hawaii was proclaimed on 4 July 1894 and recognized by Cleveland on 7 August. Cleveland was hostile to the annexation of the archipelago, but his successor, William McKinley, signed a treaty of annexation on 16 June 1897. In the Senate, however, a coalition of Democrats and anti-imperialist Republicans delayed ratification. During the Spanish-American-Cuban-Filipino War, in order to ensure uninterrupted reinforcements to Admiral Dewey in Manila, McKinley asked Congress for a joint resolution, which required only a simple majority in both houses. The resolution was passed on 7 July 1898.
The most important actions taken in this decade were linked to the war against Spain, declared on 25 April 1898. As in the war with Mexico half a century earlier, the Americans were assured of victory. French mediation paved the way for a provisional protocol, signed on 12 August. The peace conference opened on 1 October in Paris, and the peace treaty was signed on 10 December. The final treaty added the annexation of the Philippines to that of Puerto Rico, provided for in the earlier protocol. The proposed annexation of the Philippines, which had become the symbol of U.S. imperialism, provoked heated debate in the Senate. Democrats, Populists, and anti-imperialist Republicans (numerous in New England) opposed the treaty. The imperialists based their argument on national prestige and the strategic necessity of a base in the area. The Senate did not approve the Treaty of Paris until 6 Febuary 1899. The vote was 57 to 27; a change of two votes would have made it impossible to attain the necessary two-thirds majority. Guam was also acquired from Spain along with the Philippines and was important for logistical support of the army as a means of suppressing the Philippine Insurrection. Senate approval was not sought when Wake Island was similarly annexed as a war measure on 17 January 1899.