Throughout the pre-1914 period, Belgium was the main host country of the international mouvement, welcoming up to one-third of the international organizations. The Central Office of International Associations was founded in Brussels to enhance collaboration between the organizations, and to serve as a centre for documentation.

From 1903, the idea of a universal synthesis of knowledge led Otlet and La Fontaine to broaden their scope, previously focused on scientific publications. Newspapers, graphic materials and other information sources were treated in addition. To accommodate this new material, other international institutions were created. This period also saw the birth of 20th century internationalism, and Otlet and La Fontaine were fervent internationalists.

Otlet and La Fontaine established the Répertoire Bibliographique Universel (RBU), an ambitious attempt at developing a master bibliography of the world's accumulated knowledge, and at providing information for retrieval on anything of note published anywhere in the world. By the late 1930's, the RBU had grown to over 12 million entries.

The UIA can trace its origins back to 1895, when Henri La Fontaine and Paul Otlet established the International Institute of Bibliography (IIB), otherwise known as the House of Documentation (later the International Federation for Information and Documentation - FID). The IIB was the parent-organization of the Union of International Associations.

Paul Otlet was a lawyer, bibliographer, political activist and a Utopian with an internationalist agenda. His seminal work in documentation included the creation of the Universal Decimal Classification system. Otlet's concepts foreshadowed what ultimately became the World Wide Web. His vision of a network of knowledge was based on documents and included notions of hyperlinks, search engines, remote access, and networks.

La Fontaine was an international lawyer, professor of international law, and a member of the Belgian Senate for 36 years. He was a socialist, a renowned bibliographer, and a devoted internationalist. In 1913 he won the Nobel Peace Prize in recognition of his contribution towards the peace movement.