A missing horseshoe nail topples all the way to a lost kingdom, one small cause tipping into the next. It's one of the oldest cumulative rhymes in English and a neat early lesson in cause and effect.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
For want of a nail, the shoe was lost;
For want of the shoe, the horse was lost;
For want of the horse, the rider was lost;
For want of the rider, the battle was lost;
For want of the battle, the kingdom was lost,
And all for the want of a horseshoe nail.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition