Musical theatre is a form of theatrical performance that combines songs, spoken dialogue, acting, and dance. The story and emotional content of a musical – humor, pathos, love, anger – are communicated through the words, music, movement and technical aspects of the entertainment as an integrated whole. Although musical theatre overlaps with other theatrical forms like opera and dance, it may be distinguished by the equal importance given to the music as compared with the dialogue, movement and other elements. Since the early 20th century, musical theatre stage works have generally been called, simply, musicals.Although music has been a part of dramatic presentations since ancient times, modern Western musical theatre emerged during the 19th century, with many structural elements established by the works of Gilbert and Sullivan in Britain and those of Harrigan and Hart in America. These were followed by the numerous Edwardian musical comedies and the musical theatre works of American creators like George M. Cohan. The Princess Theatre musicals and other smart shows like Of Thee I Sing (1931) were artistic steps forward beyond revues and other frothy entertainments of the early 20th century and led to such groundbreaking works as Show Boat (1927) and Oklahoma! (1943). Some of the most famous and iconic musicals through the decades that followed include West Side Story (1957), The Fantasticks (1960), Hair (1967), A Chorus Line (1975), Les Misérables (1985), The Phantom of the Opera (1986), Rent (1996), The Producers (2001) and Wicked (2003).