Complex sentence: Modern historians have concluded that the fire was actually positive in terms of city development, as the pre-fire city center was extremely crowded, consisting mostly of old and cramped wood housing with only rudimentary sanitary facilities.
Split into simpler sentences: Modern historians have concluded that the fire was actually positive in terms of city development. The pre-fire city center was extremely crowded, consisting mostly of old and cramped wood housing with only rudimentary sanitary facilities.