Hay returned to the public service in 1896 when the new President-elect McKinley appointed him ambassador to Great Britain. He was offered the post of Secretary of State, while the United States negotiated the peace agreement with Spain after winning the Spanish-American War. He accepted the offer and entered service in September 1898. The evacuation of Cuba and the surrender of Puerto Rico were immediately apprehended. Spain insisted that the United States take over the Cuban debt. It was not until 21 October, three weeks after the first meeting, that Spain made its first point and agreed to take over the debt. The composition of the U.S. commission was somewhat unusual in that three of its members were senators, which, as many newspapers have pointed out, meant that they would vote later on the ratification of their own negotiations.  These were members of the American delegation: to finance the war, Congress passed an excise duty on long-distance telephone services. At that time, it was only for wealthy Americans, who were the only ones who could afford to own phones.
However, the legislators did not cancel the tax after the end of the war; it was maintained until 1 August 2006. On April 11, 1898, President William McKinley asked Congress to authorize an end to fighting in Cuba between the rebels and the Spanish armed forces and to form a “stable government” that would “maintain order” and ensure the “peace and security” of Cuban and American citizens on the island. On April 20, the U.S. Congress passed a joint resolution recognizing Cuba`s independence, urged the Spanish government to give up control of the island, intended for the United States to annex Cuba, and authorized McKinley to take whatever military measures he deemed necessary to guarantee Cuba`s independence. After the war, the United States entered a period of strong economic and demographic growth, coupled with rapid technological advances that continued until the 1920s. Hay had a significant influence on the direction of U.S. foreign policy when he served in President McKinley`s office. He was confronted with the consequences of the Spanish-American war and the annexation of the Philippines, which reinforced the United States` interest in Asia. After ten weeks of difficult negotiations, Spain and the United States finally signed the Treaty of Paris on December 10, 1898, officially ending the Spanish-American War. The 14-week conflict, described as a “great little war” by U.S.
Ambassador John Hay in a letter to his friend (and war hero) Theodore Roosevelt, is perhaps America`s least known war and certainly one of its most controversial.