What is the main conflict in The Metaphysical Club: A Story of Ideas in America by Louis Menand?

The Metaphysical Club discusses how the American thought processes in law, science, philosophy and religion were changed by four people. This way of thinking lasted until the beginning of the Cold War. The book is divided in to five parts plus a prologue and epilogue. The prologue prepares the reader and gives a short history that led to this new way of thinking.