Complex sentence: The Society suffered during the French occupation of the Netherlands in the late 18th and early 19th century, and during the bombardment of Rotterdam in May 1940 most of the archival material was lost.
Split into simpler sentences: The Society suffered during the French occupation of the Netherlands in the late 18th and early 19th century. During the bombardment of Rotterdam in May 1940 most of the archival material was lost.