Final answer:
The significant role in the decline of the Etruscan civilization was played by the towns of Rome, due to the conquest of Veii, and Carthage, due to its involvement in the broader regional conflicts.
Step-by-step explanation:
The two towns that played a significant role in the Etruscan decline are Rome and Carthage. The fall of the Etruscan city of Veii to Rome in 396 BCE marked a significant turning point in Etruscan dominance in the Italian peninsula. Additionally, by the year 474 BCE, the Greek city-state of Syracuse had become a significant power in the region after defeating the Etruscan fleet at the Battle of Cumae. Carthage's role is highlighted by its involvement along with Syracuse in the Punic Wars, which represented the broader struggle for dominance that included Sicily and affected the political and military landscape to which the Etruscans were exposed.