union, league, alliance

(れんごう) An alliance of independent organizations (usually politics, unions, or crime)
(きょうかい) A labor union.
(どうめい) An alliance, league, union (used with military things:NATO, UN Security Treaty nations, the Warsaw Pact alliance, etc.)
(れんめい) A federation: unlike 連合 and 同盟, 連盟 is made of individual people, not federated nations or gangs. Volunteers. Baseball clubs, Chess associations, the League of Women Voters, are 連盟.