What is the theme of "Forgetting," a poem in her book "A Map to the Next World"?

Joy Harjo's "Forgetting" is a reflection on history, particularly the tragedies that occurred as a result of colonialism and imperialism.
Harjo begins the poem by stating that "It will be easy enough to forget how to breathe" because it is "an acquired skill" and is motivated "by animal need" (lines 1-2). This is an odd statement since breathing is not something we think about but something we do instinctively. She uses this example to set to up a contrast to things that are not so easy to forget.
The speaker "sense[s] the shape and intent of the field of hurt  / and it's larger than the earth" (7-8). What she cannot forget, she implies, is a long history of oppression and genocide.
The speaker alludes to the English colonization of India; she feels a "raw shiver" (11) as she reflects on that example as well as "all the bad things / that have ever been done" (13-14). She suggests these "bad things" began with "the first thief to cross over / into the nation of the heart" (15-16). She again refers to the colonizer in negative terms, using the word "thief," obviously in reference to the way native lands were stolen and appropriated by Europeans. The speaker later refers to a figure similar to the thief: "the stranger in cowboy boots / among a crowd of saris and sandals" (19-20). Given the imagery here, and the use of the word "stranger," it is he who is the intruder, though he feels he is entitled to their land "of ancient miracles" (21).
Thinking about all of the subsequent tragedy, violence, and oppression that resulted from these events, the speaker "disappear[s] into the mirror of sadness" (24). It is revealed at the end of the poem that the speaker is a new mother. Her musings may be brought on by thinking about her child's place in a world that she clearly sees as flawed. Raising a child has given her, or maybe has merely enhanced, a more global perspective. It is a somewhat bleak poem, though the speaker's position is relatable and universal.