Complex sentence: He and Katniss prepare to fight as it becomes clear that a rebellion is about to begin; however, Katniss (along with Peeta) are selected for the Third Quarter Quell and must leave District 12 to return to the Games.
Split into simpler sentences: He and Katniss prepare to fight as it becomes clear that a rebellion is about to begin. However, Katniss, along with Peeta, are selected for the Third Quarter Quell and must leave District 12 to return to the Games.