 Philosophical proponents of progress assert that the human condition has improved over the course of history and will continue to improve. Doctrines of progress first appeared in 18th-century Europe and epitomize the optimism of that time and place.  Belief in progress flourished in the 19th century.  While skeptics of progress did exist alongside its supporters from the beginning, it was not until the 20th century that theorists backed away en masse from the notion.  Many 20th-century thinkers rejected the notion of progress after horrendous events such as the two World Wars, the Holocaust, and the use of nuclear weaponry. 