A LITTLE BIT OF RECENT MUSIC HISTORY
A long time ago, I was studying to be a Musicologist (which is a fancy word for a Music Historian) with an emphasis in the history of music during the twentieth century. During my studies (which came to a rather abrupt halt when I ran into a school named UT), I found myself having to create my own study aides (such as the timeline above) because the information I needed just wasn't available. When I was in school (at that college which shall not be named), I actually had to abandon normal classes and embark on independent study courses where I taught myself because no one had the necessary expertise to teach what I needed to learn.
So, in order to learn the music of the twentieth century, I created the above timeline.
Now, by way of explanation and to simplify what is alot of information above, its easy to understand that the history of music during the twentieth century is the history of musical "-isms".
The two main trends of music during the 19th century were Romanticism and Nationalism so the twentieth century begins with what is known as Post-Romanticism. This Post-Romanticism then branches off into Expressionism (Arnold Schoenberg), Impressionism (Claude Debussy), and Primitivism (the Folk-Tune/Rhythmic music of Igor Stravinsky and Bela Bartok). Expressionism evolved into Serialism while Impressionism and Primitivism lead into Neo-Classicism. Over in the USSR, they had Soviet Socialist Realism (Dimitri Shostakovitch). Neo-Classicism lead quite naturally into Neo-Romanticism (Ralph Vaughn Williams in England and Samuel Barber in America). Serialism went over the deep end and lead to a whole school of Experimentalism until the backlash of Minimalism brought things back to the simple. Neo-Romanticism spawned American Populism (as exemplified by Aaron Copland). And finally Experimentalism, Minimalism, Primitvism, and aspects of Neo-Romanticism combined to form Modernism (Elliott Carter and John Adams in America).
As can be seen by the above timeline, the music of the twentieth century is a vast canvas with a literal ton of music being composed, most of which hasn't been heard by the general public (or serious music students) or studied by historians.
Time will tell the true tale of the Twentieth Century.