In Orwell's essay Why I Write (http://orwell.ru/library/essays/wiw/english/e_wiw), published in Gangrel magazine in 1946, he points out four reasons that authors take up the pen:
1. ego: "a desire to be talked about, to be remembered after death"
2. aesthetic enthusiasm: "Pleasure in the impact of one sound or another, in the firmness of good prose or rhythm of a good story"
3. historic impulse: "find out true facts and store them up for the use of posterity"
4. political purpose: "a desire to push the world in a certain direction"
It wasn't until 1936, after the outbreak of the Spanish Civil War, however, that Orwell found a definite purpose for his writing. "Every line of serious work that I've written since 1936 has been written directly or indirectly against totalitarianism and for democratic socialism..." explained the famous author. The political theme is evident in Animal Farm, published in 1945, and Nineteen Eighty Four, published in 1949.
Note: Why I Write is listed as one of the Best American Essays of the Century by Joyce Carol Oates https://books.google.ca/books/about/The_Best_American_Essays_of_the_Century.html?id=XY1jAAAAMAAJ&redir_esc=y.