Diplomatic career
In 1890, Jackson began his long diplomatic career when President Benjamin Harrison appointed him second secretary of the legation in Germany under U.S. Minister William Walter Phelps. Four years later, President Grover Cleveland appointed him secretary of the embassy in Berlin, where he served until 1902, spending twelve years in the country under four different administrations. In 1898, he traveled from Berlin to The Hague to be present at the ceremonies in connection with the accession of Wilhelmina of the Netherlands. In March 1902, Jackson wrote to Secretary of State John Hay regarding Prince Henry of Prussia's successful visit to the U.S., speculating that it will "foster improved relations between the United States and Germany." While secretary of the legation, he frequently served, for a cumulative total of twenty months, as chargé d'affaires ad interim in charge of the embassy. His tenure included the last month of the Spanish–American War, the Hague Convention of 1899 and during the height of the Boxer Rebellion in China.
Following his service in Germany, President Theodore Roosevelt appointed Jackson U.S. Minister to Greece, Romania and Serbia on October 13, 1902, during a recess of the U.S. Senate. He was recommissioned on December 8, 1902, after confirmation. Also on October 13, 1902, he was appointed Minister to Chile, but declined appointment. He presented his credentials in Greece on December 24, 1902, in Romania on April 7, 1903, and in Serbia on May 9, 1904. While a resident of Athens as Minister to Greece, in addition to his responsibilities in Romania and Serbia, he was concurrently appointed as Minister to Bulgaria on June 5, 1903, and Montenegro on March 8, 1905. He presented his credentials in Bulgaria on September 19, 1903, and in Montenegro on October 30, 1905. In September 1904, he represented the United States at the coronation of King Peter I of Serbia.
On July 1, 1907, he was appointed Minister to Persia, presenting his credentials on December 12, 1907, and serving there until he left his post on July 3, 1909. On December 21, 1909, he was appointed Minister to Cuba, presenting his credentials on March 22, 1910, and serving until he presented his recall on October 27, 1911, and returning to the Balkans. On August 12, 1911, shortly before his recall from Havana, he was again appointed Minister to Romania, Serbia and Bulgaria, however this time he was a resident at Bucharest. In February 1912, he was the special representative of the president with rank of ambassador at Sofia for the coming of age of the Crown Prince Boris of Bulgaria. After the Democratic president Woodrow Wilson became president in 1913, Jackson submitted his resignation, as was customary, and it was accepted in August 1913, leaving Bucharest in the end of October 1913. He was succeeded by Charles J. Vopicka.
