The repetition of the letter "p" in these lines creates a blunt, harsh tone, implying perhaps that the speaker feels aggrieved by the memory of being "possessed" by the English, and by the idea of not possessing the land that was rightfully theirs to possess.

An example of assonance can be found in these lines:

Until we found out that it was ourselves
We were withholding from our land of living,
And forthwith found salvation in surrender.
Such as we were we gave ourselves outright

In these lines, Frost repeats the "ou" diphthong (a diphthong is the name for the sound produced by two consecutive vowels) seven times. This "ou" sound is a long, drawn out sound, and its repetition here creates a slow, calm tone, which echoes the calmness of the speaker at this point in the poem. Indeed, at this point in the poem, the speaker is reflecting on the collective insurgence of the American people to take possession of the land that was rightfully theirs. This is a memory which the speaker seems to find much more soothing than the aforementioned memory of being dispossessed by the English.