He spent the first few years in the United States meeting important contributors to American music, promoting his vision of new electronic music instruments, conducting orchestras, and founding the New Symphony Orchestra. It was also around this time that Varèse began work on his first composition in the United States, Amériques, which was finished in 1921. It was at the completion of this work that Varèse founded the International Composers' Guild, dedicated to the performances of new compositions of both American and European composers, for which he composed many of his pieces for orchestral instruments and voices, specifically Offrandes in 1922, Hyperprism in 1923, Octandre in 1924, and Intégrales in 1925.
In 1928, Varèse returned to Paris to alter one of the parts in Amériques to include the recently constructed Ondes Martenot. Varèse followed Amériques by composing his most famous non-electronic piece in 1930 entitled Ionisation, the first piece to feature solely percussion instruments. Although it was composed with pre-existing instruments, Ionisation was composed as an exploration of new sounds and methods to create them. In 1933, while Varèse was still in Paris, he wrote to the Guggenheim Foundation and Bell Laboratories in an attempt to receive a grant to develop an electronic music studio. His next composition, Ecuatorial, completed in 1934, contained parts for theremins, and Varèse, anticipating the successful receipt of one of his grants, eagerly returned to the United States to finally realize his electronic music.
Varèse wrote his Ecuatorial for two fingerboard Theremins, bass singer, winds and percussion in the early 1930s. It was premiered on April 15 1934, under the baton of Nicolas Slonimsky. Then Varèse left New York City, where he had lived since 1915, and moved to Santa Fe, San Francisco and Los Angeles. By the time Varèse returned in late 1938, Leon Theremin had returned to Russia. This devastated Varèse, who had hoped to work with Theremin on a refinement of his instrument. Varèse had also promoted the theremin in his Western travels, and demonstrated one at a lecture at the University of New Mexico in Albuquerque on November 12 1936. The University of New Mexico has an RCA theremin, which may be the same instrument.
When, in the late 1950s, Varèse was approached by a publisher about making Ecuatorial available, there were very few theremins -- let alone fingerboard theremins -- to be found, so he rewrote/relabelled the part for Ondes Martenot. This new version was premiered in 1961.