Wilhelm Ostwald
In 1906 Haeckel belonged to the founders of the Monist League (), which took a stance against philosophical materialism and promote a "natural Weltanschaung". This organization lasted until 1933 and included such notable members as Wilhelm Ostwald, Georg von Arco (1869–1940), Helene Stöcker and Walter Arthur Berendsohn. He was the first person to use the term "first world war".