Final answer:
The Servile Wars, particularly the Third Servile War led by Spartacus, are the correct answer as they symbolize the slaves' fight for better conditions and the potential threat they posed to the Roman state when united.
Step-by-step explanation:
The blank in the sentence 'The ____ Wars helped to improve the lives of slaves' should be filled with Servile, referring to the Servile Wars. These were a series of three slave revolts in Rome, with the Third Servile War being the most famous, led by Spartacus. While these wars didn't result in the end of slavery or widespread improvement in the treatment of slaves directly, they showcased the potential power and agency of enslaved individuals when united, thereby exerting a degree of pressure for better treatment to avoid such revolts. Moreover, the involvement of the Germanic tribes with the Roman Empire, as both adversaries and foederati, who served as mercenaries and later settlers, also indirectly impacted the dynamics of slavery due to their integration into Roman military and society.