Final answer:
The event being referenced is the Peloponnesian War, where Athenians contemplated aiding a helot revolt against Sparta, but later refrained from doing so.
Step-by-step explanation:
The historical event being referred to in the context of a helot revolt in Sparta, where the Athenians were initially inclined to help but eventually rebuked, is the Peloponnesian War (a). This war, lasting from 431 BCE to 404 BCE, was primarily fought between the Spartan-led Peloponnesian League and the Athenian Empire. Throughout the war, the Spartans received significant support from the Persians, and after many battles and shifts in power, including a disastrous Athenian expedition to Sicily and revolts among helot populations, Sparta was able to decisively defeat the Athenian navy and force Athens to surrender.
Moreover, during the aftermath of the war, Sparta's reliance on helot labor and the weakening of their military system following battles like the one at Leuctra, as well as their dwindling power even after their victory over Athens, marked a period of significant change in Greek politics and society.