After traveling to Europe, Fish returned to America and supported Abraham Lincoln as the Republican candidate for president in 1860. During the American Civil War, Fish raised money for the Union war effort and served on Lincoln's presidential commission that made successful arrangements for Union and Confederate troop prisoner exchanges. Fish returned to his law practice after the Civil War, and was thought to have retired from political life. When Ulysses S. Grant was elected president in 1868, he appointed Fish as U.S. Secretary of State in 1869. Fish took on the State Department with vigor, reorganized the office, and established civil service reform. During his 8-year tenure, Fish had to contend with Cuban belligerency, the settlement of the "Alabama" claims, Canada–US border disputes, and the "Virginius" incident. Fish implemented the new concept of international arbitration, where disputes between countries were settled by negotiations, rather than military conflicts. Fish was involved in a political feud between Senator Charles Sumner and President Grant in the latter's unsuccessful efforts to annex the Dominican Republic. Fish organized a naval expedition in an unsuccessful attempt to open trade with Korea in 1871. Leaving office and politics in 1877, Fish returned to private life and continued to serve on various historical associations. Fish died quietly of old age in his luxurious New York State home in 1893.