States minister to Spain. He took advantage of this period, 1883-85, to study still more thoroughly Spanish law, and to master the Spanish language—attainments which served him in his future professional duties as plenipotentiary in negotiating treaties and adjusting difficulties between various governments. While in Spain he negotiated a commercial treaty with that government by which he sought better opportunities for citizens of the United States in trade with Cuba and Porto Rico; but the United States senate failed to confirm the treaty, and President Cleveland who had succeeded President Arthur, at once withdrew the document for reconsideration. Minister Foster had resigned in March, 1885, but President Cleveland at once renewed his commission with full power to continue the negotiations for a treaty of reciprocity, hoping that the Spanish government would modify some of the terms to which the United States senate had objected; but in this mission he was unsuccessful for the time, although in 1891 he concluded an acceptable treaty.
On his return to the United States in 1885, Mr. Foster resumed the practice of international law at the national capital. His prestige at once gave him clients from all the countries he had visited as minister or commissioner and from other countries which had learned of his fame as a diplomat. He served as counselor for the Republic of Mexico, for the Empire of China; Spain, Chile, and other countries made him their law adviser on various occasions. His income from the practice of international law is understood to be very large. In 1890 he was appointed by President Harrison a special United States plenipotentiary to negotiate reciprocity treaties with Brazil, France, Germany, Austria, Spain, the British West Indies, and Santo Domingo, beside other of the South American republics. He made favorable treaties with all the governments with which he negotiated, except Venezuela and Colombia.
In June, 1892, on the resignation of James G. Blaine as secretary of state in the cabinet of President Harrison, the president appointed Mr. Foster to the vacancy, and he was sworn in June 29, 1892, and held the portfolio of state until the close of Harrison's administration, March 4, 1893.
He was attorney for the United States in preparing and conducting the case of the Bering Sea seal fisheries controversy with Great Britain, and he submitted the case of the United States to the tribunal created by the treaty of arbitration signed February 29,
