What are the reasons for the early documentary photography?

With the wide application of the realistic function of photography, photographers aim at human social life. People find that photography can be used to record reality and promote social progress. Thus, documentary photography came into being.

The word "documentary" was first mentioned around 1898. This year, an article was published in the British Photography Magazine, urging the establishment of a large-scale photo archive "so as to contain as complete a record as possible about the current situation of the world", claiming that such photos "will be the most valuable documentary photos in a hundred years".