Patriotism and War
The speaker reflects on the idea that he is supposed to be participating in war for the sake of patriotism. Within this framework, allegiance to one's country drives self-sacrifice, including perhaps the sacrifice of one's own life. However, the speaker doesn't have the ability to access or buy into this ideal of patriotic self-sacrifice, because the country and people he comes from aren't part of the grand drama of war. While powerful nations can fight wars on their own behalf, the speaker is fighting on behalf of another country, because his own is not sovereign: under British rule, Irish people fought wars on behalf of the British government. Patriotism, then, at least as it is commonly understood, is reserved for those who already have a measure of power.
Death
One of the more surprising elements of this work is how little the speaker seems to fear death. His attitude is accepting and resigned. To him, death is an inevitability, and one that may as well come sooner rather than later. This orientation is clear even from the poem's title: the verb "foresees" suggests not that he fears, imagines, or even waits for death, but rather that he simply perceives it in his future. His neutrality around death seems to come from a feeling that he has nothing in particular to live for, and indeed nothing in particular to die for. This is linked to his identity as an Irishman: since he is oppressed, poor, and has little control over his life, there is little that death can take from this speaker.
Irish History
Like much of Yeats's work, this poem laments the suffering and disempowerment of Ireland's people under British control. In this case, Yeats takes on this problem by describing the life and death of a single individual—a young man fighting for the British military in World War I. In fact, the poem originally responded to the death of Robert Gregory, the son of Yeats's friend Lady Augusta Gregory. Through the story of this doomed airman, Yeats discusses the injustice of young Irishmen fighting in a war from which they will not benefit. He also suggests that there is a class-based and regional element to the oppression of the Irish: the speaker specifically mentions being from a rural area in western Ireland, and mentions his affinity for the poor residents of the area. These poor rural people, the poem suggests, are especially unlikely to benefit at all from this war, even as they make sacrifices to fight in it.