Complex sentence: The story is set in the future 1000 years after the Seven Days of Fire, a brought on by excessive industrialization, which destroyed industrial civilisation approximately a millennium after it began to flourish (probably sometime in the 2700s).
Split into simpler sentences: The story is set in the future 1000 years after the Seven Days of Fire, a brought on by excessive industrialization. It utterly destroyed industrial civilisation approximately a millennium after it began to flourish (probably sometime in the 2700s).