Complex sentence: Despite being outnumbered, the Western Frontier Force was able to defeat the Senussi at Wadi Senba (11-13 December 1915), Wadi Majid (25 December 1915) and Halazin (23 January 1916), which reduced the threat the Senussi now presented.
Split into simpler sentences: Despite being outnumbered, the Western Frontier Force was able to defeat the Senussi at Wadi Senba (11-13 December 1915). Two further engagements, at Wadi Majid (25 December 1915) and Halazin (23 January 1916), reduced the threat the Senussi now presented.