Sentence:  Your invitation to write about Serge Prokofieff to honor his 70 th Anniversary for the April issue of Sovietskaya Muzyka is accepted with pleasure , because I admire the music of Prokofieff ; and with sober purpose , because the development of Prokofieff personifies , in many ways , the course of music in the <WSD>Union</WSD> of Soviet Socialist Republics . 
Meaning of the word marked with <WSD> tags:  a former communist country in eastern Europe and northern Asia; established in 1922; included Russia and 14 other soviet socialist republics (Ukraine and Byelorussia and others); officially dissolved 31 December 1991