Dark Age Pierce

Dark Age is a 2019 science fiction novel by American author Pierce Brown; it is the second book of a tetralogy which continues the story of his Red Rising trilogy (2014–2016). Dark Age takes place immediately after the events of Iron Gold (2018), as the Society Remnant forces aim to take back Mercury from the Solar Republic. A sequel, Light Bringer, was released on July 25, 2023.

Source: Wikipedia