Answer:
The use of the comparing word "nor" followed by the noun elements.
The parallelism emphasizes that nothing or no one influenced him to join the war. Rather, he went from his own decision.
Step-by-step explanation:
In William Butler Yeats' poem "An Irish Airman Foresees His Death", the speaker is the unnamed protagonist of the poem. He was part of the British soldiers fighting in the war, though he did not side with either one of the warring parties.
He admitted to participating just because of the chance to fly in the sky, stating that "Those that I fight I do not hate / Those that I guard I do not love". His decision to be a part of the fight was brought by "a lonely impulse of delight", with neither law, nor duty nor any pressure from the public making him join the war.
In the poem, the use of the grammatical comparison "nor" followed by an element is used to show the parallelism in the structure. This "nor" is also used to show the different elements that are thought to be involved in his decision to join the fight.
But this parallelism further emphasizes the point that no one or nothing influenced him to join the war. Rather, he joined it on his own accord, after he "balanced all, brought all to mind, / The years to come seemed waste of breath, / A waste of breath the years behind".