WordWeb Online

1. Unite on a federal basis or band together as a league
   "The country was federalized after the civil war";
   - federate, federalise [Brit]
    
2. Put under the control and authority of a federal government
   - federalise [Brit]
    
3. Enter into a league for a common purpose
   "The republics federalized to become the Soviet Union";
   - federate, federalise [Brit]

Derived forms: federalizing, federalizes, federalized

Type of: decentralise [Brit], decentralize, deconcentrate, merge, unify, unite