George Lucas hired Williams to do the music for Empire in 1979. This time, nearly all the music was Williams' idea, as much of the music from Star Wars would be used again. However, a significant amount of music would be needed, including music for the Imperial probe droid, a Darth Vader theme, a Yoda theme, a Leia-and-Han love theme, a "battle in the snow" segment, the asteroid field segment, a Bespin theme, and some Ewok celebratory music.
Williams says he was deeply influenced by Gustav Holst's "Mars, the Bringer of War" (taken from Holst's musical suite, The Planets) and by Frederic Chopin's Piano Sonata No. 2 (also known as "The Funeral March"). "The Imperial March" is distinctly similar to both.
"The Imperial March" did NOT premiere in the movie. It was made public on April 29, 1980, three weeks before the opening of the film. This was John Williams' first concert as conductor of the Boston Pops Orchestra.
This is conductor Bramwell Tovey wielding a lightsaber as he conducts the Vancouver Symphony Orchestra in "The Imperial March".