Here Allah (swt) is informing us about some of the nations that He has destroyed.
In Surah Al-Ghashiah Allah (swt) informs us about the Overwhelming day in which no one can escape, on the other hand, there some kinds of punishment in this life before the hereafter so that tyranny would not prevail and corruption would not spread as a result people and countries do not suffer from them.
Allah (swt) mentions examples of those who have been punished precipitately in this life as the nation of Aad, Thamud and Pharaoh, saying to His Messenger (saws): O’ Muhammad, did you not see how your Master dealt with those people? Although they had a great history of urbanization and civilization, but this did not save them from Allah’s (swt) punishment so that Allah (swt) punished them severely until they became traces of reality.
أَلَمْ تَرَ (Have you not considered): literally means (did you not see) but Allah (swt) gives this expression to emphasize the truthfulness of this news to His Prophet (saws) and to draw his and our attention to the fact that the news which are received from Allah (swt) are more truthful from what we can see by our eyes because our eyes may be deceived but Allah (swt) does not tell us but the truth that matches what the eyes see.