Yeats' poem "An Irish Airman Foresees His Death" discusses the speaker's feelings about going to war.
The speaker states that he is destined to die "among the clouds" as he participates in a war that he doesn't even want. He says he doesn't hate the enemy nor does he love those he defends. He lets us know that he was not forced to participate—he chose to fight. It was not exactly duty that caused him to join: "Nor law, nor duty bade me fight." He is not bound by law, nor is he compelled to join the service by crowds of people who see soldiers as heroes. Thus, it is "a lonely impulse of delight" that spurs his decision. He claims he thought about it ("I balanced all") so it's interesting that he calls his decision an impulse, when in fact, it's really not. He seems to have weighed his options carefully before taking this route. His choice allows him to fly "in the clouds," which brings him happiness.
We wonder why the speaker would enlist when he clearly is not feeling extremely patriotic. He gives us a hint: his life would have been a "waste." Death in war seems much more important to him than a boring life. In comparison, he'd rather have that glorious death in war than the mundane life he is anticipating leading. "A waste of breath the years behind/ In balance with this life, this death."
The reader must consider that Yeats is being sarcastic. The soldier does not reveal any wish to go to war, but he ironically calls his decision a "delight." Does the speaker really believe that his life would have been so boring that he'd rather die in war? Is Yeats commenting on the consequences of going to war? He repeats the phrase "waste of breath" twice, forcing us to consider that this is indeed an anti-war poem and not an acceptance of death poem.