Complex sentence: During the first years of the Second World War he was with his division involved in many campaigns and battles, the most autonomous operation being the occupation of the northern provinces of The Netherlands in May 1940, leading to the Battle of The Afsluitdijk.
Split into simpler sentences: During the first years of the Second World War he and his division were involved in many campaigns and battles. The division's most notable, and independent action being that of the occupation of the northern provinces of The Netherlands in May 1940, leading to the Battle of The Afsluitdijk.