What did the term "white man's burden" mean?

This term comes from a poem by Rudyard Kipling and means that it was on the shoulders of a white man to maintain civilized societies. And that it was a task of white Americans to create an Empire just like Europeans Empires.

The term "white man" is explained due to the beliefs of that time. People were extremely racist and they believed that black men had reduced mental capacities and could not maintain a functional society.

This was not considered racism because at that time people really believed that there were two races - white and black and that the white race was better.