"The White Man's Burden" was specifically written to urge the United States to take up what Kipling viewed as its duty to annex and "civilize" the Philippines after the Spanish-American War. So the entire poem is essentially about imperialism. In one line early in the poem, Kipling urges his readers to "send your sons to exile/to serve your captives' need." Here Kipling imagines empire as a service to what he perceives as primitive peoples, "captives" who "need" Anglo-American civilization. He develops this premise further when he claims that those who would claim empires should do it to "seek another's profit/and work another's gain."
Kipling goes on to refer to "new-caught, sullen peoples" that have recently been brought into the American empire (itself a novel concept) as a result of the war. These people, imagined in the racialized language common in Kipling's day as "half-devil and half-child," will not understand, according to Kipling's paternalist view, that what is being done is for the best. Thus the rewards of empire-building will be "the blame of those ye better/the hate of those ye guard," but those who take up the challenge will also receive the "judgment of your peers." These quotes directly reference the imperialist project upon which the United States was about to embark at the turn of the century, and they reveal much about the highly racist, often contradictory assumptions that undergirded colonialism.