Coincidentally (perhaps), 151 years ago today, on June 13, 1856, Yeats took his first breath in Dublin. Yeats believed that history unfolds in 2,000 year cycles and the poem imagines a rather dark transition to a new era, which the poet felt was already underway at the time of its writing in 1920. Certainly in the aftermath of World War I there was an apocalyptic dread gripping all of Europe.
Although I don't believe in such a tidy cyclical reading of history, I do believe that we are in the midst of a threshold moment. The old order is slipping away, and new forces are emerging that will define what takes its place. Yeats saw the dark potential for this changing of the guard, as the "rough beast ... slouches toward Bethlehem." That threat is evident today with the prevailing portents of catastrophic climate change, pandemics, and wars wrought by religious and ideological extremists.
Along with those reasons for pessimism, however, there is a great opportunity to remake our world in a positive way based on the powerful technologies arising. The potential is there for a truly democratic, healthy and sustainable society, but it's something we'll have to work very hard to win.
The Wikipedia article on the poem has some interesting background detail. Here is the full text:
The Second Coming
TURNING and turning in the widening gyre
The falcon cannot hear the falconer;
Things fall apart; the centre cannot hold;
Mere anarchy is loosed upon the world,
The blood-dimmed tide is loosed, and everywhere
The ceremony of innocence is drowned;
The best lack all conviction, while the worst
Are full of passionate intensity.
Surely some revelation is at hand;
Surely the Second Coming is at hand.
The Second Coming! Hardly are those words out
When a vast image out of Spiritus Mundi
Troubles my sight: somewhere in sands of the desert
A shape with lion body and the head of a man,
A gaze blank and pitiless as the sun,
Is moving its slow thighs, while all about it
Reel shadows of the indignant desert birds.
The darkness drops again; but now I know
That twenty centuries of stony sleep
Were vexed to nightmare by a rocking cradle,
And what rough beast, its hour come round at last,
Slouches towards Bethlehem to be born?