The twentieth century brought with it numerous changes to life, two great wars, breaking down of long standing class hierarchy bring a freedom. In music, the freedom and fundamental changes came in the uses of rhythm. The influences of other areas of the world freed composers to explore the importance of rhythm proofing that rhythm is the musical pulse. Stravinsky, the first to demonstrate musical change through rhythm as portrayed in his Rite of Spring. The journey continues with the works of Gustav Mahler, Steve Reich, and Pierre Boulez as well as others. It has the most breath-taking ending with composer Olivier Messiaen, a WWII POW, composition that is an extreme, emotional, control celebration of life.