Complex sentence: He started writing at the urging of Edward Bawden, another artist, but at the outbreak of war in 1939 he wriote to the War Artists Advisory Commission offering his services as an artist.
Split into simpler sentences: He started writing at the urging of Edward Bawden. Another artist, but at the outbreak of war in 1939 he wriote to the War Artists Advisory Commission offereiong hios services as an artist.