Complex sentence: From Eton, Bevan attended Christ Church, Oxford until the outbreak of World War I. Then, in August 1914, he left to join the Hertfordshire Regiment of the Territorial Force.
Split into simpler sentences: From Eton, Bevan went up to Christ Church, Oxford until the outbreak of the First World War. In August 1914, he left to join the Hertfordshire Regiment of the Territorial Force.