Twentieth Century Music is the third volume to appear in this series. Morgan divides his text into three chronological sections. Beginning with such giants as Mahler, Richard Strauss and Debussy, he discusses national movements, as represented by Charles Ives and Ralph Vaughan Williams; philosophical movements as various as the Schoenberg/Berg/Webern alliance or "les six"; and the giants who were "sui generis", such as Bartok and Stravinsky. The "isms" such as serialism, minimalism, indeterminism, the new romanticism and pluralism, are clearly delineated and the electronic boom of the last decades is defined.
Best book I have seen on that market that covers post WWII music in a holistic setting. I wish more emphasis was on composers of the 90s, but considering that my copy dates to 1991, the lack is understandable. Integral serialism, indeterminacy, stochastic music, minimalism, musique concrete and bad boys like Stockhausen, Babbitt, and Cage are given a proper treatment, something lacking considering knee jerk reactionary opinions that dub their experiments as "noise".
This is a great resource for 20th century European and American music that shows the evolution from Romantic to modern. What I like about this book is that it starts each era with a general look at the political, cultural, and artistic climate of each era that puts the music in its proper context.