Complex sentence: The city experienced a second, much larger building boom that lasted from the early 1970s to late 1980s, during which time it saw the construction of six skyscrapers, including the Kettering Tower and KeyBank Tower.
Split into simpler sentences: The city experienced a second, much larger building boom that lasted from the early 1970s to late 1980s. During this time, Dayton saw the construction of six skyscrapers, including the Kettering Tower and KeyBank Tower.