Complex sentence: The union was recognized by the United Kingdom, France and Italy in the Treaty of Paris (1920), which nevertheless did not come into force as Japan, one of the signatories, failed to ratify it.
Split into simpler sentences: The union was recognized by the United Kingdom, France and Italy in the Treaty of Paris (1920). The treaty did not, however, come into force as Japan, one of the signatories, failed to ratify it.