Allah (swt) clarifies the legions that they are the people of Pharaoh and Thamood who are the people of the Prophet Salih (Peace be Upon Him).
We notice the accuracy of the Quranic expression: Pharaoh is a single person whereas Thamood is the name of a tribe. That is to indicate that the whole tribe was against the prophet Salih (Peace be upon him) whereas some of Pharaoh’s tribe believed the Prophet Moses (Peace be upon him) but Pharaoh is the one who led the people to enmity and claimed that he is a god and his people believed and obeyed him. However, we note that who denied the Messenger of Allah (saws), with their keenness to deny and their eagerness to skirmish, did not stop at this issue and they never spoke about what happened with Pharaoh and Thamud. This indicates that they knew it well but they concealed the truth and lied and became insolent with great insolence. This is a warning to Quraish: who are you in comparison of the powers of Pharaoh and Thamood!! Yet look what happened to them and what Allah (swt) has done to them.