同盟【どうめい】
alliance, union, league
加盟【かめい】
joining (an association, agreement, etc.), participation, affiliation, accession
連盟【れんめい】
league, federation, union, alliance
盟約【めいやく】
oath, pledge, pact, covenant, alliance
盟友【めいゆう】
sworn friend
盟主【めいしゅ】
leader (of an alliance), leading power
同盟条約【どうめいじょうやく】
treaty of alliance
期成同盟【きせいどうめい】
association formed to carry out an objective