That history was revised in Genesis of the Daleks (1975), which revealed the detailed origin of the Daleks. The name of the Dals was changed to the Kaleds, who were a fascistic society involved in a generations-long war of attrition with the Thals (whose use of slave labour did not make them much better). The prolonged conflict had turned Skaro into a wasteland, and radiation sickness was a common hazard. The Kaled chief scientist, Davros, accelerated the mutation of the Kaled species and put the results into tank-like travel machines, which became the dreaded Daleks.
In The Daleks, the Doctor helped the Thals defeat the Daleks on Skaro, apparently returning them to a peaceful age before he left.
At some point, the Thals established a space-faring civilisation. In Planet of the Daleks (1973), set in Earth's 26th century, and several generations after the events of The Daleks, a Thal expedition was sent to the planet Spiridon. Together, the Thals and the Third Doctor defeated a Dalek plan to duplicate the natural invisibility of the planet's inhabitants and launch a ten-thousand strong Dalek army hidden on the planet. What happened to the Thals after this is not revealed in the series, though in Destiny of the Daleks (1979) Skaro was shown to be an abandoned planet. Skaro was destroyed in Remembrance of the Daleks (1988), when the Seventh Doctor sent the Omega Device to the future to destroy the Dalek/Thal homeworld, although nothing further has been noted about the Thals after the aforementioned Spiridon encounter.