One result of the decline of the british empire was

the development of realism
the development of anxiety
the development of romanticism
the development of existentialism

One result of the decline of the British Empire was the development of Realism. In the US authors like Mark Twain dealt with the truth and explored accepted conventions. As opposed to the Romantics, who probably had a positive image of the world as exemplified by the highest sensibilities of mankind, the Realists in literature were probably more prone to talk of the way  things actually are even if they are not_glorious events as Romantics may have emphasized..