When  Yeats wrote "The Second Coming" the world had just come through the worst conflagration of all time, The Great War. The changes that were wrought by that awful conflict are too many to number - suffice it to say - Europe was never the same again. So it is understandable that Yeats might see how  "mere anarchy is loosed upon the world."

Yeats second coming has little do with the Biblical version. He had developed a complex mystical system of gryres - these are spirals or vortices - that worked in such a way to determine great changes in history. I am doing his thinking no justice here, merely pointing out that we are not in Christian territory. Yeats felt that a change was coming and he uses the image of the sphinx, after "twenty centuries of stony sleep" a creature that has been "vexed to nightmare by a rocking cradle" to symbolise it.

It is easy to think that we are in times unlike any other and that a giant something is just around the corner. The "end times" have often been mooted, always incorrectly. Still, there may be more to it this time. Never has humankind had the ability to so comprehensively destroy itself. Never before. This is alien country.

And when things do fall apart, often as not, " the centre cannot hold."