Schumann wrote:There were many great Spanish composers: Albeniz, Falla, Granados, Mompou. I can't really believe that you've never heard of them!
I know Granados and Albeniz, but they are really obscure. Albeniz wrote a famous tango, and Granados wrote one or two songs of note. I think what was said about guitar music is more in line with what came from Spain.
I tend to think of Germany, Austria, Russia, Norway, France, Poland, and The United States as the principal countries of classical music (the U.S. came into play later on.) Ironically, there were few English composers, Elgar being an exception.
The absolute must have composers for the archive though would probably be:
J. S. Bach - Ger
L. V. - Beethoven Ger?
W. A. Mozart - Aus?
J. Brahms - Ger
R. Strauss - Ger
P. I. Tchaikovsky - Rus
G. F. Handel - Eng?
J. Haydn - Ger?
G. Bizet - Fra
I. Stravinsky - Rus
F. Mendelsson - Ger
R. Wagner - Ger
H. Berlioz - Fra
J. Strauss - Aus?
C. W. Gluck - Ger
G. Meyerbeer - Fra
F. Chopin - Pol?
F. Liszt - Hun
F. Schubert - Ger?
And later on:
S. Prokofiev - Rus
J. Williams - USA
H. Zimmer - Ger
M. Steiner - USA
L. Bernstien - USA
D. Shostakovich - Rus
I probably missed alot, but the absolute essentials are listed, specifically Bach, Beethoven, Mozart, and Tchaikovsky.