Complex sentence: Prior to this year, the women's race was usually held at the Henley Boat Races along the course, although on at least two occasions, in the interwar period, the women competed on the Thames between Chiswick and Kew.
Split into simpler sentences: Prior to this year, the women's race was usually held at the Henley Boat Races along the course. However, on at least two occasions in the interwar period, the women competed on the Thames between Chiswick and Kew.