Complex sentence: At the beginning of 1918, the division was attached to XX Corps and helped to capture Jericho (19--21 February) and then formed part of Shea's Force for the First Trans-Jordan Raid (21 March--2 April).
Split into simpler sentences: At the beginning of 1918, the division was attached to XX Corps and helped to capture Jericho (19--21 February). It then formed part of Shea's Force for the First Trans-Jordan Raid (21 March--2 April).