Analysis of I Hear an Army Charging Upon the Land

I hear an army charging upon the land,
  And the thunder of horses plunging, foam about their knees:
Arrogant, in black armour, behind them stand,
  Disdaining the reins, with fluttering whips, the charioteers.

They cry unto the night their battle-name:         
  I moan in sleep when I hear afar their whirling laughter.
They cleave the gloom of dreams, a blinding flame,
  Clanging, clanging upon the heart as upon an anvil.

They come shaking in triumph their long, green hair:
  They come out of the sea and run shouting by the shore.  
My heart, have you no wisdom thus to despair?
  My love, my love, my love, why have you left me alone?