Complex sentence: By mid-April, the small British force at Kohima was relieved, and from 18 April to 13 May, British and Indian reinforcements counter-attacked to drive the Japanese from the positions they had captured.
Split into simpler sentences: By mid-April, the small British force at Kohima was relieved. From 18 April to 13 May, British and Indian reinforcements counter-attacked to drive the Japanese from the positions they had captured.