The encyclical was not the first Catholic writing on industrial conditions. Bishop Wilhelm Emmanuel von Ketteler in Mainz, the Fribourg Union, and a scatter of French and Belgian social Catholics had been arguing these questions for decades, and much of their language reaches the text directly. What Leo XIII added was standing. A pope had now said it, at length, in a document addressed to the whole Church.
The immediate effect was institutional. Catholic trade unions, cooperatives and mutual societies multiplied across Germany, Belgium, Italy and later Latin America with a document they could point to. Christian democratic parties in the twentieth century traced their economic programme to it. In the United States it shaped the labour advocacy of John A. Ryan and, through him, several New Deal arguments.
The other effect was to create a genre. Pius XI marked the fortieth anniversary in 1931 with Quadragesimo Anno, which introduced the principle of subsidiarity. John XXIII marked the seventieth with Mater et Magistra, Paul VI wrote Populorum Progressio in 1967, and John Paul II marked the hundredth with Centesimus Annus in 1991, which reassessed the whole tradition after the fall of the Eastern bloc. Each is written as a commentary on the one before, and all of them are dated from 1891.
That chain is why the atlas files the encyclical as an instrument rather than only as a text. It did not merely say something; it established a form of saying it that the institution has used ever since.