Federate (verb)

1. To unite or join (a number of states, organizations, etc.) under a federal government or system.
2. To form a federation, as a group of states or other entities.

Origin:

Mid 17th century: from latin foederat- "allied by treaty", from the verb foederare, from foedus "treaty".

Examples:

1. The country decided to federate with its neighboring countries.
2. The organization decided to federate with other similar organizations.
3. The states voted to federate and form a new country.
4. The different tribes decided to federate to protect their mutual interests.
5. The decision to federate was made to increase their bargaining power.