Question: Who was American, Gustave Charpentier or Samuel Barber or both? 

Context articles: Du style galant au style méchant
Jacques Charpentier
String Quartet (Barber)
Julien (opera)
Louise (opera)
Symphony No. 2 (Barber)
Cello Concerto (Barber)
Gustave Charpentier
Samuel Barber
Konstantinos Papadakis (pianist)

Du style galant au style méchant is an opera cycle written for radio by composer Germaine Tailleferre and librettist Denise Centore.
 The cycle uses four short one act French language chamber operas, each one written to parody a different operatic form or style.
 These operas are La fille d'opéra (a parody of Jean-Philippe Rameau), Le bel ambitieux (a parody of Giacomo Rossini), La pauvre Eugénie (a parody of Gustave Charpentier), and Monsieur Petit Pois achète un château (a parody of Jacques Offenbach).
 The cycle had its world premiere on December 28, 1955 in a performance by the Radiodiffusion-Télévision Française.
Jacques Charpentier (October 18, 1933 in Paris, France – June 15, 2017 in Lézignan-Corbières) was a French composer and organist.
 He is unrelated to either of two other eminent French musicians with the same surname (Marc-Antoine Charpentier and Gustave Charpentier).
The String Quartet in B minor, Op. 11 was written in 1935–36 by Samuel Barber.
 Barber arranged the middle movement for string orchestra as his well-known "Adagio for Strings" in 1936.
 Barber continued to revise the piece, particularly the finale, until 1943.
Julien, ou La vie du poète ("Julien, or The Poet’s Life") is a poème lyrique or opera by composer Gustave Charpentier.
 The work is devised in a prologue and four acts and uses a French libretto by the composer.
 "Julien" is a sequel to Charpentier's "Louise" (1900) and describes the artistic aspirations of Louise’s suitor Julien.
 The opera premiered in Paris at the Opéra-Comique on 4 June 1913.
Louise is an opera ("roman musical" ) in four acts by Gustave Charpentier to an original French libretto by the composer, with some contributions by Saint-Pol-Roux, a symbolist poet and inspiration of the surrealists.
Symphony No. 2, Op. 19 is a three-movement work for orchestra by American composer Samuel Barber.
 The 25-minute work was originally written in 1944.
 The work underwent many revisions and was finally published in 1950.
 The original manuscript was withdrawn by Barber in 1964.
 He ordered that G. Schirmer destroy the original manuscript and all scores in their library.
 The work remained unpublished for many years until 1984 when a set of parts turned up in a warehouse in England.
 Renewed interest in Barber's work led to a 1990 reprint of the 1950 edition.
Samuel Barber's Concerto for Violoncello and Orchestra in A minor, Op.
 22, completed on 27 November 1945 , was the second of his three concertos (the first being his Violin Concerto and the third his Piano Concerto).
 Barber was commissioned to write his cello concerto for Raya Garbousova, an expatriate Russian cellist, by Serge Koussevitzky on behalf of Garbusova and the Boston Symphony Orchestra.
 Funds for the commission were supplied, however, by John Nicholas Brown, an amateur cellist and a trustee of the Boston Symphony Orchestra .
 The score is dedicated to John and Anne Brown .
 Barber was still on active duty with the U. S. Army at the time he received the commission, and before beginning work asked Garbousova to play through her repertoire for him so that he could understand her particular performing style and the resources of the instrument .
 Garbousova premiered it with the Boston Symphony Orchestra in Symphony Hall, Boston, on 5 April 1946, followed by New York performances at the Brooklyn Academy of Music on 12 and 13 April .
 The concerto won Barber the New York Music Critics' Circle Award in 1947 .
Gustave Charpentier (] ; 25 June 1860 – 18 February 1956) was a French composer, best known for his opera "Louise".
Samuel Osborne Barber II (March 9, 1910 – January 23, 1981) was an American composer of orchestral, opera, choral, and piano music.
 He is one of the most celebrated composers of the 20th century: music critic Donal Henahan stated that "Probably no other American composer has ever enjoyed such early, such persistent and such long-lasting acclaim."
Konstantinos Papadakis (Greek: Κωνσταντίνος Παπαδάκης ; born October 2, 1972 in Heraklion, Crete, Greece) is a Greek pianist.
 He has received the Golden Medal of superior talent.
 He has performed in worldwide major concert halls such as Carnegie Hall and Wigmore Hall.
 He studied with Anthony di Bonaventura at Boston University.
 Three years later, he joined the piano faculty at Boston University and was later appointed a "Samuel Barber" Artist in Residence at West Chester University of Pennsylvania where he remained for 5 years.
 In 2011 he joined the piano faculty of the New England Conservatory's Pre-College Division in Boston.
 He holds the prestigious Motoko and Gordon Deane Principal Chair of Boston's Atlantic Symphony Orchestra.
 He has premiered many works, including Samuel Barber's "Three Essays", "Three Sketches", "Fresh from West Chester" and "Fantasy for two pianos".
 The "Boston Globe" has described him as "one of the greatest hopes of music".
 Celebrating the bicentennial year of Franz Liszt, he released a recording with short miniatures for piano entitled "The Short Liszt" to a critical acclaim.
 He is the director of the AASMA Piano Summer Academy in Archanes Crete, Greece.
 In 2013 was appointed lecturer at  Boston University College of Fine Arts.