The Second Coming by W.B. Yeats (1920)

Turning and turning in a widening gyre, the falcon climbs until it can no longer hear the falconer, and the world it once circled comes loose at the centre. That is the first thing the poem hands you, and it is already the whole nightmare: not the violence, but the failure of whatever had been holding violence back. The famous line lands like a verdict the century would spend a hundred years confirming, the centre cannot hold, the best paralysed by doubt while the worst burn with conviction. Then the poem turns from diagnosis to vision, and the vision offers no comfort. Out of the desert a shape stirs, lion-bodied, its gaze blank and pitiless as the sun, moving with terrible patience toward the town where the redeemer was once born. Read it once and the last image stays for life: some rough beast, its hour come round at last, slouching toward Bethlehem to be born.