Final answer:
The Peloponnesian War between Athens and Sparta left the Greek Civilization weak and open to invasion.
Step-by-step explanation:
The war between Athens and Sparta that left the Greek Civilization weak and open to invasion was the Peloponnesian War. This war lasted from 431-404 BCE and was fought between the two leading city-states in ancient Greece, Athens and Sparta. It was a result of long-standing tensions between these two powers and their respective allies. The Peloponnesian War significantly weakened Athens and left it vulnerable to invasion.