The historical development of Continental philosophy's existentialism and phenomenology in response to Hegelian idealism can be traced back to the late nineteenth and early twentieth centuries and pre-Socratics. While philosophers often disagree, it is quite apparent that the key contributors to the rise in existentialism and phenomenology had extensive disagreements with Hegelian idealism and is quite clear in their writings. I think it is important to first understand existentialism and phenomenology, and finally the key contributors.
Existentialism is the idea that the most important question in philosophy is how to live. With that, it states that any philosophical method that takes something else as primary is unacceptable. Existentialism was first seen in the late twentieth century in the works of Arthur Schopenhauer (1788-1860), Soren Kierkegaard, and finally Friedrich Nietzsche. These three men had a strong dislike for the optimistic idealism of Hegel--truly though, for any metaphysical system in general. The three men also felt that such philosophy ignored the human predicament.
Not only did these men feel that such philosophy ignored the human predicament, they also felt that the universe, including all humans, is seldom rational and that philosophical systems that only seek to make everything seem rational are merely useless attempts to conquer pessimism and despair.
Soren Kierkegaard ridiculed Hegel's system wherein the individual dissolves into an abstract unreality and he emphasized the human being and in particularly the human being's will and need to make important choices. Friedrich Nietzsche later read the workings of Arthur Schopenhauer and became increasingly and thoroughly convinced that the world is driven by cosmic will and not that of reason. He also snubbed Hegel's idealism and any similar rationalist metaphysics; however, he began to disagree with the disposition of cosmic will of Schopenhauer. He later claimed that the world is driven by and...