In 1870 he served in the National Guard during the Franco-Prussian war. After the war he continued to compose, and he became professor of composition at the Conservatoire. He spent many years working on an opera "Le Roi de Lahore". This was a great success and helped him to become internationally famous. For many years he spent the winter in Paris and the summer in various places in the country where he could compose. His pupils at the Conservatoire included Pierné, Koechlin, Hahn, Enesco. In 1884 his opera "Manon" was produced at the Opéra-comique. This made him clearly the most famous opera composer of his time. It was an opéra-comique with some speech over the music. During the next 28 years he composed another 20 operas. Another opera that was particularly famous was "Werther". It was first performed in 1892 in Vienna and a year later in Paris. It was soon being performed in all the big European opera houses.