federalize

(verb) unite on a federal basis or band together as a league. Synonyms: federate, federalise. Example: "The country was federated after the civil war."

(verb) put under the control and authority of a federal government. Synonyms: federalise.

(verb) enter into a league for a common purpose. Synonyms: federate, federalise. Example: "The republics federated to become the soviet union."