It's right there in the word you used: millennium. The referent is truly ancient. Ancient Zoroastrianism held that history is a cycle of periods of 1000 years, each ending in heresy in destruction. Judaism and Christianity inherited this concept, and there have always been strains of Christian millennialism, the most literal of which hold that Christ will rule on Earth for literally 1000 years, until the last judgment. That is why it is resonant.