Hamburg Philharmonic Orchestra, from 1898 onwards Fiedler was active abroad as a guest conductor, appearing in Russia, where he was compared to Artur Nikisch and Felix Weingartner, Madrid (1899), Paris (1901), Turin (1904), Rome (1906, 1908) and London (1907, 1908). Throughout this period he developed a reputation as a major interpreter of the music of Brahms, as well as a conductor with ‘complete mastery’ of the orchestra. In 1908, Karl Muck, then the conductor of the Boston Symphony Orchestra, recommended Fiedler as his successor as conductor of the orchestra, and he was duly appointed, having already appeared in the United States during 1905, when he had conducted the New York Philharmonic Orchestra alongside Willem Mengelberg and a year before the guest appearance of a German conductor noted for his Brahms, Fritz Steinbach. Although he spent four years at the helm in Boston, his conducting attracted some criticism, especially for his volatility as an interpreter, which was viewed as pleasing ‘the general public’ rather than ‘connoisseurs’. Among his achievements there, he conducted the world premiere of Paderewski's massive [[Symphony in B minor (Paderewski)|Symphony in B minor "Polonia]] in 1909. Fiedler returned to Hamburg in 1912, where Siegmund von Hausegger was now in charge of the Philharmonic Orchestra; and since co-residence was likely to be difficult, given his own status as a former conductor of this orchestra, Fiedler withdrew to Berlin, where he became an active guest conductor of the city's various orchestras. In 1916 a Berlin critic hailed him as ‘the greatest Brahms conductor of the present day’, and during the same year he accepted the position of conductor of the Essen Orchestra, in succession to Hermann Abendroth, who was moving to Cologne to replace Steinbach. At Essen, Fiedler consolidated his reputation as a major figure in German musical life, conducting a wide repertoire that included contemporary composers such as Walter Braunfels, Karol Szymanowski and Arthur Honegger, as well as each year organising a festival devoted to a major single composer. In addition he guest-conducted the Berlin Philharmonic occasionally, and from 1927 was co-conductor of the Essen Folkwangschule. In 1929 he married for the second time and in 1934 gave up his position in Essen, returning once more to Berlin where he conducted the Berlin Radio Orchestra, as well as that of Hamburg. During 1939 he made a series of farewell appearances in Berlin and Essen, but towards the end of