see also NOAH
In the preceeding verses, we are told that the people denied Noah and laughed at him, so Noah called upon God for help. As a result the flood came and destroyed them. see the next item.
Surah Nuh tells us that Noah was sent to warn his people, to ask them to serve Allah and keep their duties to Him and obey Noah, that Allah may forgive of their sins (what kind, the Qur'an didn't say). Noah's call resulted in greater repugnance and pride, persisting in their own gods, and because of their sins they were drowned. Noah called upon Allah not to leave any disbeliever in the land (Nuh 71:26).