How does Phyllis McGinley use imagery in The Conquerors?

Imagery:

When one remembers how for years,
With their rude stones and humble spears,
Our sires, at wiping out their peers

The Greeks got excellent results
With swords and engined catapults.
A chariot served the Roman.
Mere cannon garnered quite a yield
On Waterloo's tempestuous field.
At Hastings and at Flodden
Stout countrymen, with just a bow
And arrow, laid their thousands low.