The better aphoristic horse-kingdom-related summation is probably For Want Of A Nail:

  For want of a nail the shoe was lost.
  For want of a shoe the horse was lost.
  For want of a horse the rider was lost.
  For want of a rider the message was lost.
  For want of a message the battle was lost.
  For want of a battle the kingdom was lost.
  And all for the want of a horseshoe nail.