First, I don't think we can find any literature that is not responsive or reactive to the past, literary history, artistic precursors, etc. Even the science fiction of the 20th century was reacting to the adventure stories that came before it (Westerns, Pirate stories, Military epics, etc). So, yes, modernism was a response to earlier literary movements. (...maybe you have something more specific in mind with your question regarding "a reaction to traditional literature" that I am not seeing right away...)
Secondly, modernism, as I understand it, was the first literary/arts movement to present the notion of subjective truth as a replacement for absolute "real" truth. Truth became defined by personal experience in modernism, which also emphasized a personal relationship to history.
Postmodernism and modernism are not completely different in their regard for and presentations of truth.
Look at the modernist works like Faulkner's As I Lay Dying and you see a work with many perspectives on truth and reality. Look at Hemingway's Sun Also Rises and you see a very personalized understanding of moral truth, social truth and hopeful truth.