Complex sentence: The "official war artists" of the First World War created a unique account of that conflict; and the British War Artists Scheme (WAS) expanded the number of official artists and enlarged the scope of their activities during the Second War.
Split into simpler sentences: The "official war artists" of the First World War created a unique account of that conflict. The British War Artists Scheme (WAS) expanded the number of official artists and enlarged the scope of their activities during the Second War.