Complex sentence: Kinglassie's development during the late 19th and early 20th Century was marked by its rapid expansion to house mine workers, many mine workers perished and were injured during the mines lifetime and the mine was plaqued by water flooding problems.
Split into simpler sentences: Kinglassie's development during the late 19th and early 20th Century was marked by its rapid expansion to house mine workers. Many mine workers perished and were injured during the life of the mine--the mine was plagued by water flooding problems.