During the First World War, Wittgenstein served in the army and developed his logic. He included ethical aspects. In the summer of 1918 he learned that his friend David Pinsent had been killed in an airplane accident. Wittgenstein became depressed and thought of suicide. He went to stay with his uncle Paul where he was able to complete the "Tractatus". No publisher accepted it, but Russell realised it was a philosophically important work and wrote an introduction. Wittgenstein did not like it because he thought that Russell had not understood the book. In the end Wilhelm Ostwald's journal "Annalen der Naturphilosophie" printed a German edition in 1921, and Routledge's Kegan Paul printed a bilingual edition with Russell's introduction in 1922.