"Mere anarchy is loosed upon the world, The blood-dimmed tide is loosed, and everywhere The ceremony of innocence is drowned;" (lines 4-6)
These lines have often been interpreted as a description of the apocalyptic war described in the Book of Revelation, when an army of angels takes on Satan and his henchmen. This climatic battle has been depicted many times in popular culture, such as by the authors of the Left Behind book series. But we think no one has produced a sense of "Last Days" terror quite like W.B. Yeats with this metaphor of a bloody, rushing tide. Of course, in this battle, the innocent are defeated, so maybe it’s just the prelude to an even bigger war.
"Surely the Second Coming is at hand." (line 10)
In the Book of Revelation, the Second Coming of Christ is foreshadowed by centuries of violence, chaos, and bloodshed.
"twenty centuries of stony sleep Were vexed to nightmare by a rocking cradle" (lines 19-20)
These words have proven truer than Yeats probably intended (unless you believe that he really did have clairvoyant powers!). There have been many violent centuries in the last two thousand years, but seemingly none as chaotic and destructive as the 20th century. These lines chillingly combine hints of warfare with images of infancy.