"How many have We destroyed," meaning: We punished, "before them," referring to the disbelievers of Mecca, up to His saying: "and We destroyed them for their sins." He is warning the polytheists of the Arabs and frightening them with that by which He destroyed the nations when they denied their messengers, "and We brought forth"—meaning: We created—"after them another generation."
Muhammad said: It is said: A generation (qarn) is eighty years.