This passage is a commentary on what era in united states and world history?

Here is the passage:

The White Man's Burden
Rudyard Kipling, 1899

Take up the White Man's burden--
Send forth the best ye breed--
Go bind your sons to exile
To serve your captives' need;
To wait in heavy harness,
On fluttered folk and wild--
Your new-caught, sullen peoples,
Half-devil and half-child.

Take up the White Man's burden--
In patience to abide,
To veil the threat of terror
And check the show of pride;
By open speech and simple,
A hundred times made plain
To seek another's profit,
And work another's gain.

This passage is a commentary on what era in the United States and World History?
The passage is about  European imperialism in the nineteenth and early twentieth centuries.