federalise

Verb
  1. Put under the control and authority of a federal government (synset 200505545)
  2. Enter into a league for a common purpose (synset 200370095)
    "The republics federated to become the Soviet Union"
  3. Unite on a federal basis or band together as a league (synset 200369847)
    "The country was federated after the civil war"

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