Final answer:
The Greeks united in defense of their culture and way of life due to shared cultural bonds and the external threat posed by the Persian Empire, leading to a collective response during the Persian Wars.
Step-by-step explanation:
What caused the Greeks to unify in defense of their culture and way of life can be attributed to multiple factors. Although Greek city-states, known as poleis, were fiercely independent and often at odds with each other, they shared common bonds such as language, religion, and culture.
These bonds were reinforced through Panhellenic sanctuaries and festivals, like the Olympics, that promoted a sense of collective Greek identity. The threat of foreign domination, particularly during the Persian Wars, was a pivotal factor that galvanized these city-states to unite against a common enemy to defend their shared Hellenic lifestyle and autonomy.
The Greeks also saw themselves as cultural equals, participating in cultural practices, trading, raiding, and settling alongside other civilizations. Eventually, as parts of Greek civilization fell under Persia's influence in the sixth century BCE, the Greek city-states found a greater cause to join forces in what culminated in the full-scale war against Persia.
This unity in diversity became a hallmark of Greek civilization and contributed to its lasting influence across the Mediterranean world and the Middle East.