Complex sentence: Munro remained on the family farm until the end of the First World War, when his father sold the farm while Munro worked on the Otira Tunnel construction until recalled to work with his father on a newly purchased farm.
Split into simpler sentences: Munro remained on the family farm until the end of the First World War, when his father sold the farm. At the time, Munro worked on the Otira Tunnel construction until recalled to work with his father on a newly purchased farm.