Complex sentence: In May 1917, nearly three years since the outbreak of the First World War, Stephenson enlisted in the Royal Field Artillery and saw action on the Western Front and later served as part of the British Army of the Rhine.
Split into simpler sentences: In May 1917, nearly three years since the outbreak of the First World War, Stephenson enlisted in the Royal Field Artillery and saw action on the Western Front. He later served as part of the British Army of the Rhine.